UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

FORM N-CSR

CERTIFIED SHAREHOLDER REPORT OF REGISTERED
MANAGEMENT INVESTMENT COMPANIES

ITEM 1. REPORT TO STOCKHOLDERS.

The Annual Report to Stockholders is filed herewith.

Annual Report

Western Asset Investment Grade Defined Opportunity Trust Inc.
(IGI)

Fund objectives

The Fund’s primary investment objective is to provide current income and then to liquidate and distribute substantially all of the Fund’s net assets to stockholders on or about December 2, 2024. As a secondary investment objective, the Fund will seek capital appreciation. There can be no assurance the Fund will achieve its investment objectives.

What’s inside

Dear Shareholder,

We are pleased to provide the annual report of Western Asset Investment Grade Defined Opportunity Trust Inc. for the twelve-month reporting period ended November 30, 2012. Please read on for a detailed look at prevailing economic and market conditions during the Fund’s reporting period and to learn how those conditions have affected Fund performance.

Recent regulations adopted by the Commodity Futures Trading Commission (the “CFTC”) require operators of registered investment companies, including closed-end funds, to register as “commodity pool operators” unless the fund limits its investments in commodity interests. Effective December 31, 2012, your Fund’s manager has claimed the exclusion from the definition of “commodity pool operator.” More information about the CFTC rules and their effect on the Fund is included later in this report on page 40.

As always, we remain committed to providing you with excellent service and a full spectrum of investment choices. We also remain committed to supplementing the support you receive from your financial advisor. One way we accomplish this is through our website, www.lmcef.com. Here you can gain immediate access to market and investment information, including:

·  Fund prices and performance,

·  Market insights and commentaries from our portfolio managers, and

·  A host of educational resources.

We look forward to helping you meet your financial goals.

Investment commentary

Economic review

While the U.S. economy continued to grow over the twelve months ended November 30, 2012, it did so at an uneven pace. U.S. gross domestic product (“GDP”)i growth, as reported by the U.S. Department of Commerce, was 4.1% in the fourth quarter of 2011. Economic growth in the U.S. then decelerated, as first quarter 2012 GDP growth was 2.0%. This was primarily due to less robust private inventory and non-residential fixed investments. The economy slowed further in the second quarter, as GDP growth was a tepid 1.3%. GDP growth then moved to 3.1% in the third quarter. The increase was partially due to increased private inventory and investment, higher federal government spending and a deceleration in imports.

The U.S. job market remained weak. While there was some improvement during the reporting period, unemployment remained elevated. When the reporting period began, unemployment, as reported by the U.S. Department of Labor, was 8.5%. Unemployment then generally declined and was 8.1% in April 2012, the lowest rate since January 2009, but still high by historical standards. The unemployment rate then rose to 8.3% in July, before falling to 7.8% in September and ending the reporting period at 7.7% in November. However, the number of longer-term unemployed remained high, as roughly 40% of the 12 million people without a job have been out of work for more than six months.

Meanwhile, the housing market brightened, as sales have started to improve of late and home prices continued to rebound. According to the National Association of Realtors (“NAR”), existing-home sales rose 5.9% on a seasonally adjusted basis in November 2012 versus the previous month and they were 14.5% higher than in November 2011. In addition, the NAR reported that the median existing-home price for all housing types was $180,600 in November 2012, up 10.1% from November 2011. This marked the ninth consecutive month that home prices rose compared to the same period a year earlier. Furthermore, the inventory of homes available for sale fell 3.8% in November, which represents a 4.8 month supply at the current sales pace. This represents the lowest inventory since September 2005.

The manufacturing sector appeared to overcome a soft patch that occurred in the summer of 2012 as it improved toward the end of the reporting period, only to experience another setback in November 2012. Based on the Institute for Supply Management’s PMI (“PMI”)ii, after expanding 34 consecutive months, the PMI fell to 49.7 in June 2012, which represented the first contraction in the manufacturing sector since July 2009 (a reading below 50 indicates a contraction, whereas a reading above 50 indicates an expansion). Manufacturing continued to contract in July and August before ticking up to 51.5 in September and 51.7 in October. However, the PMI fell back to contraction territory with a reading of 49.5 in November, its lowest level since July 2009.

The Federal Reserve Board (“Fed”)iii took a number of actions as it sought to meet its dual mandate of fostering maximum employment and price stability. As has been the case since December 2008, the Fed kept the federal funds rateiv at a historically low range between zero and 0.25%. In September 2011, prior to the beginning of the reporting period, the Fed announced its intention to purchase

Investment commentary (cont’d)

$400 billion of longer-term Treasury securities and to sell an equal amount of shorter-term Treasury securities by June 2012 (often referred to as “Operation Twist”). In January 2012, the Fed extended the period it expects to keep rates on hold until at least through late 2014. Operation Twist was then extended in June 2012 until the end of the year. In September the Fed announced a third round of quantitative easing, which involves purchasing $40 billion each month of agency mortgage-backed securities (“MBS”) on an open-end basis. In addition, the Fed said that Operation Twist would continue and that it will keep the federal funds rate on hold until at least mid-2015. Finally, at its meeting in December, after the reporting period ended, the Fed announced that it would continue purchasing $40 billion per month of agency MBS, as well as initially purchasing $45 billion a month of longer-term Treasuries. The Fed also said that it would keep the federal funds rate on hold “...as long as the unemployment rate remains above 6.5%, inflation between one and two years ahead is projected to be no more than a half percentage point above the Committee’s 2.0% longer-run goal, and longer-term inflation expectations continue to be well anchored.”

As always, thank you for your confidence in our stewardship of your assets.

All investments are subject to risk including the possible loss of principal. Past performance is no guarantee of future results.

i                Gross domestic product (“GDP”) is the market value of all final goods and services produced within a country in a given period of time.

ii             The Institute for Supply Management’s PMI is based on a survey of purchasing executives who buy the raw materials for manufacturing at more than 350 companies. It offers an early reading on the health of the manufacturing sector.

iii          The Federal Reserve Board (“Fed”) is responsible for the formulation of policies designed to promote economic growth, full employment, stable prices and a sustainable pattern of international trade and payments.

iv           The federal funds rate is the rate charged by one depository institution on an overnight sale of immediately available funds (balances at the Federal Reserve) to another depository institution; the rate may vary from depository institution to depository institution and from day to day.

Fund overview

Q. What is the Fund’s investment strategy?

A. The Fund’s primary investment objective is to provide current income and then to liquidate and distribute substantially all of the Fund’s net assets to stockholders on or about December 2, 2024. As a secondary investment objective, the Fund will seek capital appreciation. There can be no assurance the Fund will achieve its investment objectives.

The Fund seeks to achieve its investment objectives by investing, under normal market conditions, at least 80% of its net assets in investment grade corporate fixed-income securities of varying maturities. The Fund may invest up to 20% of its net assets in corporate fixed-income securities of below investment grade quality at the time of investment and other securities, including obligations of the U.S. government, its agencies or instrumentalities, common stocks, warrants and depositary receipts. While the Fund may invest up to 20% of its net assets in below investment grade securities, the Fund will, under normal market conditions, maintain a portfolio with an overall dollar-weighted average of investment grade credit quality. The Fund may invest up to 20% of its net assets in securities of foreign issuers located anywhere in the world, including issuers located in emerging market countries. Additionally, the Fund may invest up to 20% of its net assets in non-U.S. dollar denominated securities.

The Fund may invest in derivative instruments, such as options contracts, futures contracts, options on futures contracts, indexed securities, credit default swaps and other swap agreements, provided that the Fund’s exposure to derivative instruments, as measured by the total notional amount of all such instruments, will not exceed 20% of its net assets.

In purchasing securities and other investments for the Fund, we may take full advantage of the entire range of maturities and durationsi offered by corporate fixed-income securities and may adjust the average maturity or duration of the Fund’s portfolio from time to time, depending on our assessment of the relative yields available on securities of different maturities and durations and our expectations of future changes in interest rates.

The Fund may take on leveraging risk by utilizing certain management techniques, whereby it will segregate liquid assets, enter into offsetting transactions or own positions covering its obligations. To the extent the Fund covers its commitment under such a portfolio management technique, such instrument will not be considered a senior security for the purposes of the Investment Company Act of 1940. However, as a fundamental policy, the Fund will not leverage its capital structure by issuing senior securities such as preferred shares or debt instruments.

At Western Asset Management Company (“Western Asset”), the Fund’s subadviser, we utilize a fixed-income team approach, with decisions derived from interaction among various investment management sector specialists. The sector teams are comprised of Western Asset’s senior portfolio management personnel, research analysts and an in-house economist. Under this team approach, management of client fixed-income portfolios will reflect a consensus of interdisciplinary views within the Western Asset organization.

Fund overview (cont’d)

The individuals responsible for development of investment strategy, day-to-day portfolio management, oversight and coordination of the Fund are Stephen A. Walsh, Michael C. Buchanan and Ryan K. Brist.

Q. What were the overall market conditions during the Fund’s reporting period?

A. The spread sectors (non-Treasuries) experienced periods of volatility during the reporting period, but ultimately posted positive results. Demand for the spread sectors was generally robust during the first three months of the reporting period. This was due to several factors, including signs that the U.S. economy was gathering momentum and some progress in the European sovereign debt crisis. However, fears that the economy may be experiencing a soft patch and contagion fears from Europe led to periods of heightened risk aversion during portions of March, April and May 2012. The spread sectors then largely rallied from June through November as investor sentiment improved.

Short-term Treasury yields were unchanged, whereas long-term Treasury yields declined during the reporting period. When the period began, two-year Treasury yields were 0.25%. They moved as low as 0.21% on January 17, 2012 and as high as 0.41% on March 20, 2012. Ten-year Treasury yields were 2.08% at the beginning of the period and peaked at 2.39% on March 19, 2012. On July 25, 2012, ten-year Treasuries closed at an all-time low of 1.43%. Yields then edged higher due to some positive developments in Europe and hopes for additional Federal Reserve Board (“Fed”)ii actions to stimulate the economy. When the reporting period ended on November 30, 2012, two-year Treasury yields were 0.25% and ten-year Treasury yields were 1.62%.

All told, the Barclays U.S. Aggregate Indexiii returned 5.51% for the twelve months ended November 30, 2012. Comparatively, the Barclays U.S. Credit Indexiv (the “Index”) returned 11.59% over the same period.

Q. How did we respond to these changing market conditions?

A. A number of adjustments were made to the Fund’s portfolio during the reporting period. We reduced the Fund’s exposure to high-yield bonds given their strong performance. From a sector perspective, we increased the Fund’s allocations to Capital Goods1, Consumer Cyclicals2 and Consumer Non-Cyclicals3, while paring its allocation to Energy. Finally, we increased the Fund’s exposure to BBB-rated investment-grade corporate bonds.

During the reporting period, U.S. Treasury futures were used to manage the Fund’s duration and yield curvev positioning. As of the end of the period, the duration of the Fund was marginally shorter (less sensitive to changes in interest rates) than its benchmark. The use of Treasury futures to reduce the interest sensitivity of the Fund detracted from performance. However, we more than made up for

1              Capital Goods consists of the following industries: Aerospace & Defense, Building Materials, Diversified Manufacturing, Construction Machines, Packaging and Environmental.

2              Consumer Cyclicals consists of the following industries: Automotive, Entertainment, Gaming, Home Construction, Lodging, Retailers, Restaurants, Textiles and other consumer services.

3              Consumer Non-Cyclicals consists of the following industries: Consumer Products, Food/Beverage, Health Care, Pharmaceuticals, Supermarkets and Tobacco.

the negative impact from our interest rate hedge with very strong credit sector and issuer selection during the period. The use of currency forwards to manage our currency exposure modestly contributed to results. Finally, credit default swaps, which were used to manage the Fund’s investment-grade bond exposure, slightly benefited performance during the reporting period.

Performance review

For the twelve months ended November 30, 2012, Western Asset Investment Grade Defined Opportunity Trust Inc. returned 17.12% based on its net asset value (“NAV”)vi and 17.28% based on its New York Stock Exchange (“NYSE”) market price per share. The Fund’s unmanaged benchmark, the Barclays U.S. Credit Index, returned 11.59% for the same period. The Lipper Corporate Debt BBB-Rated Closed-End Funds Category Averagevii returned 11.94% over the same time frame. Please note that Lipper performance returns are based on each fund’s NAV.

During the twelve-month period, the Fund made distributions to shareholders totaling $1.39 per share. The performance table shows the Fund’s twelve-month total return based on its NAV and market price as of November 30, 2012. Past performance is no guarantee of future results.

Performance Snapshot as of November 30, 2012

All figures represent past performance and are not a guarantee of future results.

*  Total returns are based on changes in NAV or market price, respectively.

†  Total return assumes the reinvestment of all distributions at NAV. Prior to January 1, 2012, total return assumed the reinvestment of all distributions in additional shares in accordance with the Fund’s Dividend Reinvestment Plan.

‡  Total return assumes the reinvestment of all distributions in additional shares in accordance with the Fund’s Dividend Reinvestment Plan.

Q. What were the leading contributors to performance?

A. The largest contributor to the Fund’s relative performance during the reporting period was its allocation to high-yield bonds (roughly 12.4% of the portfolio at period-end). This was rewarded given the high-yield market’s outperformance versus higher quality corporate bonds. Overall, sector positioning was positive for performance. In particular, an overweight to the Financials sector was rewarded as it significantly outperformed the Index. Within the Financials sector, we favored the Banking subsector as we felt that structural changes in this area, including greater capital requirements, less leverage and more consistent fundamental performance would be beneficial to bondholders. Our outlook for Financials in general and Banking in particular, proved accurate and helped drive the Fund’s performance.

Issue selection also enhanced the Fund’s results. Many of the strongest performers were in the Banking subsector, such as our overweights in Citigroup Inc. and Bank of America Corp. Both companies benefited from continued balance sheet and capital ratio improvements and strong fundamental results. Also within the Financials sector, overweights in

Fund overview (cont’d)

Goldman Sachs Group Inc., American International Group Inc. and General Electric Capital Corp. contributed to performance as investor sentiment for these companies improved given strengthening fundamentals.

The Fund’s ratings biases were also additive for performance. In particular, an overweight to lower-rated BBB bonds was a positive, as they outperformed the Index. In addition, we underweighted bonds rated AAA and AA, which was beneficial given their underperformance versus the Index.

Q. What were the leading detractors from performance?

A. The Fund significantly outperformed its benchmark during the reporting period. However, a few individual holdings detracted from the Fund’s relative performance, including our overweights in NewPage Corp. and Cengage Learning Acquisitions, Inc. NewPage Corp. is the largest North American maker of coated papers. When the period began, NewPage Corp. was in bankruptcy. However, we had a relatively constructive outlook for our small overweight position in its senior secured first-lien bonds, as we felt that we would negotiate a favorable recovery with the company. As the period progressed, the company’s fundamental performance continued to deteriorate and our bonds traded lower. We exited the position at roughly 51% of face value toward the end of the reporting period and bonds have since migrated lower post our sale. Cengage Learning, a text book publisher, recently posted weak fundamental results. Our small overweight to senior secured Cengage Learning Term Loans was not beneficial during the period. We believe we are trading relatively close to the secured loan recovery value today, but feel there is upside potential if the current management team can stabilize the business.

Modestly detracting from the Fund’s relative performance were its overweights to the Basic Industry1 and Energy sectors as they underperformed the Index.

Looking for additional information?

The Fund is traded under the symbol “IGI” and its closing market price is available in most newspapers under the NYSE listings. The daily NAV is available on-line under the symbol “XIGIX” on most financial websites. Barron’s and the Wall Street Journal’s Monday edition both carry closed-end fund tables that provide additional information. In addition, the Fund issues a quarterly press release that can be found on most major financial websites as well as www.lmcef.com.

In a continuing effort to provide information concerning the Fund, shareholders may call 1-888-777-0102 (toll free), Monday through Friday from 8:00 a.m. to 5:30 p.m. Eastern Time, for the Fund’s current NAV, market price and other information.

Thank you for your investment in Western Asset Investment Grade Defined Opportunity Trust Inc. As always, we appreciate that you have chosen us to manage your assets and we remain focused on achieving the Fund’s investment goals.

Sincerely,

Western Asset Management Company

December 18, 2012

1  Basic Industry consists of the following industries: Chemicals, Metals & Mining and Paper.

RISKS: The Fund’s investments are subject to credit risk, inflation risk and interest rate risk. As interest rates rise, bond prices fall, reducing the value of the Fund’s holdings. The Fund may invest in lower-rated high-yield bonds which are subject to greater credit risk (risk of default) than higher-rated obligations. The Fund may use derivatives, such as options and futures, which can be illiquid, may disproportionately increase losses and have a potentially large impact on Fund performance. The Fund may invest in securities or engage in transactions that have the economic effects of leverage which can increase the risk and volatility of the Fund.

Portfolio holdings and breakdowns are as of November 30, 2012 and are subject to change and may not be representative of the portfolio managers’ current or future investments. Please refer to pages 9 through 19 for a list and percentage breakdown of the Fund’s holdings.

The mention of sector breakdowns is for informational purposes only and should not be construed as a recommendation to purchase or sell any securities. The information provided regarding such sectors is not a sufficient basis upon which to make an investment decision. Investors seeking financial advice regarding the appropriateness of investing in any securities or investment strategies discussed should consult their financial professional. The Fund’s top five sector holdings (as a percentage of net assets) as of November 30, 2012 were: Financials (36.7%), Energy (12.4%), Consumer Discretionary (10.7%), Telecommunication Services (8.0%) and Utilities (7.4%). The Fund’s portfolio composition is subject to change at any time.

All investments are subject to risk including the possible loss of principal. Past performance is no guarantee of future results. All index performance reflects no deduction for fees, expenses or taxes. Please note that an investor cannot invest directly in an index.

The information provided is not intended to be a forecast of future events, a guarantee of future results or investment advice. Views expressed may differ from those of the firm as a whole.

i                Duration is the measure of the price sensitivity of a fixed-income security to an interest rate change of 100 basis points. Calculation is based on the weighted average of the present values for all cash flows.

ii             The Federal Reserve Board (“Fed”) is responsible for the formulation of policies designed to promote economic growth, full employment, stable prices and a sustainable pattern of international trade and payments.

iii          The Barclays U.S. Aggregate Index is a broad-based bond index comprised of government, corporate, mortgage- and asset-backed issues, rated investment grade or higher, and having at least one year to maturity.

iv           The Barclays U.S. Credit Index is an index composed of corporate and non-corporate debt issues that are investment grade (rated Baa3/BBB or higher).

v              The yield curve is the graphical depiction of the relationship between the yield on bonds of the same credit quality but different maturities.

vi           Net asset value (“NAV”) is calculated by subtracting total liabilities and outstanding preferred stock (if any) from the closing value of all securities held by the Fund (plus all other assets) and dividing the result (total investments) by the total number of the common shares outstanding. The NAV fluctuates with changes in the market prices of securities in which the Fund has invested. However, the price at which an investor may buy or sell shares of the Fund is the Fund’s market price as determined by supply of and demand for the Fund’s shares.

vii        Lipper, Inc., a wholly-owned subsidiary of Reuters, provides independent insight on global collective investments. Returns are based on the twelve-month period ended November 30, 2012, including the reinvestment of all distributions, including returns of capital, if any, calculated among the 12 funds in the Fund’s Lipper category.

Fund at a glance† (unaudited)

Investment breakdown (%) as a percent of total investments

†  The bar graph above represents the composition of the Fund’s investments as of November 30, 2012 and November 30, 2011 and does not include derivatives, such as futures contracts, written options, swap contracts and forward foreign currency contracts. The Fund is actively managed. As a result, the composition of the Fund’s investments is subject to change at any time.

Spread duration (unaudited)

Economic Exposure — November 30, 2012

Total Spread Duration

Spread duration measures the sensitivity to changes in spreads. The spread over Treasuries is the annual risk-premium demanded by investors to hold non-Treasury securities. Spread duration is quantified as the % change in price resulting from a 100 basis points change in spreads. For a security with positive spread duration, an increase in spreads would result in a price decline and a decline in spreads would result in a price increase. This chart highlights the market sector exposure of the Fund’s sectors relative to the selected benchmark sectors as of the end of the reporting period.

Effective duration (unaudited)

Interest Rate Exposure — November 30, 2012

Total Effective Duration

Effective duration measures the sensitivity to changes in relevant interest rates. Effective duration is quantified as the % change in price resulting from a 100 basis points change in interest rates. For a security with positive effective duration, an increase in interest rates would result in a price decline and a decline in interest rates would result in a price increase. This chart highlights the interest rate exposure of the Fund’s sectors relative to the selected benchmark sectors as of the end of the reporting period.

Schedule of investments

November 30, 2012

Western Asset Investment Grade Defined Opportunity Trust Inc.

See Notes to Financial Statements.

Schedule of investments (cont’d)

November 30, 2012

Western Asset Investment Grade Defined Opportunity Trust Inc.

See Notes to Financial Statements.

Western Asset Investment Grade Defined Opportunity Trust Inc.

See Notes to Financial Statements.

Schedule of investments (cont’d)

November 30, 2012

Western Asset Investment Grade Defined Opportunity Trust Inc.

See Notes to Financial Statements.

Western Asset Investment Grade Defined Opportunity Trust Inc.

See Notes to Financial Statements.

Schedule of investments (cont’d)

November 30, 2012

Western Asset Investment Grade Defined Opportunity Trust Inc.