As filed with the Securities and Exchange Commission on July 27, 2021

1933 Act File No. 333-241035

1940 Act File No. 811-23600

U.S. Securities and Exchange Commission

Washington, D.C. 20549

FORM N-2

(Check appropriate box or boxes)

Thornburg Income Builder Opportunities Trust

Exact Name of Registrant as Specified in Declaration of Trust

c/o Thornburg Investment Management, Inc.

2300 North Ridgetop Road, Santa Fe, NM 87506

Address of Principal Executive Offices (Number, Street, City, State, Zip Code)

(505) 984-0200

Registrant’s Telephone Number, including Area Code

Erin Carney, Managing Director

2300 North Ridgetop Road

Santa Fe, New Mexico 87506

Name and Address (Number, Street, City, State, Zip Code) of Agent for Service

Copies of Communications to:

Joshua B. Deringer

Faegre Drinker Biddle & Reath LLP

One Logan Square, Ste. 2000

Philadelphia, PA 19103-6996

Approximate Date of Proposed Public Offering: As soon as practicable after the effective date of this Registration Statement

It is proposed that this filing will become effective (check appropriate box)

If appropriate, check the following box:

Check each box that appropriately characterizes the Registrant:

CALCULATION OF REGISTRATION FEE UNDER THE SECURITIES ACT OF 1933

EXPLANATORY NOTE

This Registration Statement is being filed pursuant to Rule 462(b) under the Securities Act of 1933, as amended. The contents of the Registration Statement on Form N-2 (Reg. No. 333-241035) filed by Thornburg Income Builder Opportunities Trust (the “Registrant”) with the Securities and Exchange Commission, declared effective July 27, 2021, are incorporated herein by reference. On July 27, 2021, the Registrant registered 32,000,000 shares of common stock in Pre-Effective Amendment No. 5 to the Registrant’s Registration Statement filed on Form N-2. When the shares of common stock previously registered are combined with the shares of common stock registered herein, the total number of shares registered by the Registrant is 33,350,000 shares. Any required consents are listed on an Exhibit Index attached hereto and are filed herewith.

PART C - OTHER INFORMATION

Item 25: Financial Statements and Exhibits

Registrant has not conducted any business as of the date of this filing, other than in connection with its organization. Financial Statements indicating that the Registrant has met the net worth requirements of Section 14(a) of the Investment Company Act of 1940 will be filed with a Pre-effective Amendment to the Registration Statement.

Item 26: Marketing Arrangements

See Form of Underwriting Agreement, the Form of Master Selected Dealers Agreement, the Form of Closed-End Fund Distribution Services Agreement, the Form of Structuring Fee Agreement with Oppenheimer & Co. Inc., Form of Structuring Fee Agreement with RBC Capital Markets, LLC, Form of Structuring Fee Agreement with Stifel, Nicolaus & Company, Incorporated, Form of Structuring Fee Agreement with Wells Fargo Securities, LLC, Form of Structuring Fee Agreement with UBS Securities LLC, and the Form of Sales Incentive Fee Agreement filed as Exhibit (h)(1), Exhibit (h)(2), Exhibit (h)(3), Exhibit (k)(4), Exhibit (k)(5), Exhibit (k)(6), Exhibit (k)(7), Exhibit (k)(8) and Exhibit (k)(9), respectively, to the Registrant’s Registration Statement.

Item 27: Other Expenses of Issuance and Distribution

Item 28: Persons Controlled by or under Common Control with Registrant

Not applicable.

Item 29: Number of Holders of Securities

Item 30: Indemnification

Delaware law permits a Delaware statutory trust to include in its declaration of trust a provision to indemnify and hold harmless any trustee, beneficial owner or other person from and against any and all claims and demands whatsoever. Except as otherwise provided in the Trust’s declaration of trust, the Trust will indemnify and hold harmless to the fullest extent permitted by law any current or former Trustee, officer or agent of the Trust against any and all liabilities and expenses reasonably incurred or paid by them in connection with any proceeding in which they become involved by virtue of their being or having been such a trustee, agent or officer, and against amounts paid by them in the settlement thereof. In accordance with the 1940 Act, the Trust will not indemnify any Trustee, agent or officer for any liability to which such person would be subject by reason of his or her willful misfeasance, willful misconduct, bad faith, gross negligence or reckless disregard of the duties of his or her position, or if such trustee, agent or officer did not act in good faith in the reasonable belief that the action was in the best interest of the Trust. Expenses of a person entitled to indemnification may be advanced from time to time, subject to certain conditions outlined in the declaration of trust, by the Trust prior to final disposition upon receipt of an undertaking by such person that such amount will be paid to the Trust if it is ultimately determined that he or she is not entitled to indemnification.

Item 31: Business and Other Connections of Investment Advisers

The information in the Statement of Additional Information under the captions “Board of Trustees and Officers” is hereby incorporated by reference.

Item 32: Location of Accounts and Records.

Thornburg Investment Management, Inc. maintains the Declaration of Trust, By-Laws, minutes of trustees and shareholders meetings and contracts of the Registrant, all advisory material of the investment adviser, all general and subsidiary ledgers, journals, trial balances, records of all portfolio purchases and sales, and all other required records.

Item 33: Management Services

Not applicable.

Item 34: Undertakings

SIGNATURES

Pursuant to the requirements of the Securities Act of 1933 and the Investment Company Act of 1940, the Registrant has duly caused this Registration Statement to be signed on its behalf by the undersigned, thereunto duly authorized, in this City of Santa Fe, and State of New Mexico, on the 27th day of July, 2021.

Pursuant to the requirements of the Securities Act of 1933, this Registration Statement has been signed below by the following persons in the capacities and on the dates indicated.