Filed pursuant to Rule 424(b)(3)

Registration No. 333-232183

OWL ROCK CAPITAL CORPORATION II

Supplement No. 9 dated October 21, 2020

To

Prospectus dated July 1, 2020

This supplement contains information that amends, supplements or modifies certain information contained in the accompanying prospectus of Owl Rock Capital Corporation II dated July 1, 2020 as previously supplemented and amended (as so supplemented and amended, the “Prospectus”) and is part of, and should be read in conjunction with, the Prospectus. The Prospectus has been filed with the U.S. Securities and Exchange Commission, and is available free of charge at www.sec.gov or by calling (877) 822-4276. Capitalized terms used in this supplement have the same meanings as in the Prospectus, unless otherwise stated herein.

Before investing in shares of our common stock, you should read carefully the Prospectus and this supplement and consider carefully our investment objective, risks, charges and expenses. You should also carefully consider the “Risk Factors” beginning on page 32 of the Prospectus before you decide to invest in our common stock.

STATUS OF OUR PUBLIC OFFERING

Since commencing our initial public offering and through October 20, 2020, we have issued 134,891,226 shares of our common stock for gross proceeds of approximately $1.238 billion, including seed capital contributed by Owl Rock Capital Advisors LLC (the “Adviser”) in September 2016 and approximately $10 million in gross proceeds raised from certain individuals and entities affiliated with the Adviser.

RECENT DEVELOPMENTS

On October 21, 2020, we completed our previously announced offering of an additional $50 million aggregate principal amount of its 4.625% notes due 2024 (the “Notes”). The offering was consummated pursuant to the terms of a purchase agreement (the “Purchase Agreement”) dated October 9, 2020 among us and Owl Rock Capital Advisors LLC (the “Advisor”), on the one hand, and Deutsche Bank Securities Inc. and SG Americas Securities, LLC, as representatives of the several initial purchasers listed on Schedule 1 thereto (the “Initial Purchasers”), on the other hand. The Purchase Agreement provided for the Notes to be issued to the Initial Purchasers in a private placement in reliance on Section 4(a)(2) of the Securities Act of 1933, as amended (the “Securities Act”), and for initial resale by the Initial Purchasers to qualified institutional buyers pursuant to the exemption from registration provided by Rule 144A promulgated under the Securities Act. We relied upon these exemptions from registration based in part on representations made by the Initial Purchasers. The Notes have not been registered under the Securities Act and may not be offered or sold in the United States absent registration or an applicable exemption from registration. The net proceeds from the sale of the Notes were approximately $48.65 million, after deducting the fees paid to the Initial Purchasers and estimated offering expenses of approximately $850,000, each payable by us. We intend to use the net proceeds to pay down a portion of our outstanding indebtedness.

The Notes were issued as additional notes under the Indenture dated as of November 26, 2019 (the “Base Indenture”), between us and Wells Fargo Bank, National Association, trustee (the “Trustee”), and a First Supplemental Indenture, dated as of November 26, 2019 (the “First Supplemental Indenture” and together with the Base Indenture, the “Indenture”), pursuant to which we issued $300 million aggregate principal amount of the 4.625 Notes due 2024 (the “existing 2024 Notes”) on November 26, 2019. The Notes will be treated as a single series with the existing 2024 Notes under the Indenture and will have the same terms as the existing 2024 Notes. The Notes will mature on November 26, 2024, unless repurchased or redeemed in accordance with their terms prior to such date. The Notes bear interest at a rate of 4.625% per year payable semi-annually on May 26 and November 26 of each year, commencing on November 26, 2020.

The Notes will be our direct, general unsecured obligations and will rank senior in right of payment to all of our future indebtedness or other obligations that are expressly subordinated, or junior, in right of payment to the Notes. The Notes will rank pari passu, or equal, in right of payment with all of our existing and future indebtedness or other obligations that are not so subordinated, or junior. The Notes will rank effectively subordinated, or junior, to any of our future secured indebtedness or other obligations (including unsecured indebtedness that we later secure) to the extent of the value of the assets securing such indebtedness. The Notes will rank structurally subordinated, or junior, to all existing and future indebtedness and other obligations (including trade payables) incurred by our subsidiaries, financing vehicles or similar facilities.

The Indenture contains certain covenants, including covenants requiring us to (i) comply with the asset coverage requirements of the Investment Company Act of 1940, whether or not it is subject to those requirements, and (ii) provide financial information to the holders of the Notes and the Trustee if we are no longer subject to the reporting requirements under the Securities Exchange Act of 1934, as amended. These covenants are subject to important limitations and exceptions that are described in the Indenture.

In addition, if a change of control repurchase event, as defined in the Indenture, occurs prior to maturity, holders of the Notes will have the right, at their option, to require us to repurchase for cash some or all of the Notes at a repurchase price equal to 100% of the principal amount of the Notes being repurchased, plus accrued and unpaid interest to, but excluding, the repurchase date.

COVER PAGE OF PROSPECTUS

The following is added to the cover page of our prospectus:

“Securities regulators have not passed upon whether this offering can be sold in compliance with existing or future suitability or conduct standards including the ‘Regulation Best Interest’ standard to any or all purchasers.”

SUITABILITY STANDARDS

The following is added to the “Suitability Standards” section of our prospectus:

On June 5, 2019, the SEC adopted Regulation Best Interest, which establishes a new standard of conduct for broker-dealers and natural persons who are associated persons of a broker-dealer under the Securities Exchange Act of 1934, as amended (the “Exchange Act”), that enhances the standard beyond suitability. Broker-dealers must comply with Regulation Best Interest commencing June 30, 2020. Regulation Best Interest includes the general obligation that broker-dealers shall act in the “best interest” of retail customers in making any recommendation of any securities transaction or investment strategy, without putting the financial or other interests of the broker-dealer ahead of the retail customer. The general obligation can be satisfied by the broker-dealer’s compliance with four specified component obligations: (i) provide certain required disclosure before or at the time of the recommendation, about the recommendation and the relationship between the broker-dealer and the retail customer; (ii) exercise reasonable diligence, care, and skill in making the recommendation; (iii) establish, maintain, and enforce written policies and procedures reasonably designed to address conflicts of interest; and (iv) establish, maintain, and enforce written policies and procedures reasonably designed to achieve compliance with Regulation Best Interest. Like existing suitability obligations, the component obligations of Regulation Best Interest contain a quantitative standard. Such quantitative standard may be more or less restrictive pursuant to Regulation Best Interest than under the suitability standard. In addition, broker-dealers are required to provide retail investors a brief relationship summary, or Form CRS, that summarizes for the investor key information about the broker-dealer. Form CRS is different from this prospectus, which contains information regarding this offering and our company. The impact of Regulation Best Interest on broker-dealers cannot be determined at this time as no administrative or case law exists under Regulation Best Interest and the full scope of its applicability is uncertain.

RISK FACTORS

The following is added to the “Risk Factors” section of our prospectus:

Compliance with the SEC’s Regulation Best Interest by participating broker-dealers may negatively impact our ability to raise capital in this offering, which would harm our ability to achieve our investment objectives.

Commencing June 30, 2020, broker-dealers must comply with Regulation Best Interest, which, among other requirements, establishes a new standard of conduct for broker-dealers and their associated persons when making a recommendation of any securities transaction or investment strategy involving securities to a retail customer. The impact of Regulation Best Interest on participating dealers cannot be determined at this time, and it may negatively impact whether participating dealers and their associated persons recommend this offering to certain retail customers. If Regulation Best Interest reduces our ability to raise capital in this offering, it would harm our ability to create a diversified portfolio of investments and ability to achieve our investment objectives.