Filed Pursuant To Rule 424(b)(5)
Registration No. 333-263169
PROSPECTUS SUPPLEMENT DATED September 5, 2023
(To Prospectus Supplements dated May 10, 2023, February 22, 2023
and accompanying Prospectus dated March 1, 2022)
$500,000,000
HANNON ARMSTRONG SUSTAINABLE
INFRASTRUCTURE CAPITAL, INC.
Common Stock
This supplement
supplements the prospectus supplement dated February 22, 2023, as supplemented by that certain prospectus supplement dated May 10, 2023, and the accompanying prospectus dated March 1, 2022 relating to the issuance and sale of shares
of our common stock, par value $0.01 per share, or our common stock, having an aggregate offering price of up to $500,000,000 from time to time through our sales agents, B. Riley Securities, Inc., Barclays Capital Inc., BofA Securities, Inc., Credit
Suisse Securities (USA) LLC, Goldman Sachs & Co. LLC, Jefferies LLC, J.P. Morgan Securities LLC, KeyBanc Capital Markets Inc., Morgan Stanley & Co. LLC, Nomura Securities International, Inc., Truist Securities, Inc. and Wells Fargo
Securities, LLC, or the Sales Agents by means of ordinary brokers transactions on the New York Stock Exchange, or the NYSE, at market prices, in negotiated transactions or by any other method permitted by law deemed to be an at-the-market offering as defined in Rule 415 under the Securities Act of 1933, as amended, or the Securities Act, including by sales made directly on or through
the NYSE or otherwise, in negotiated transactions, which may include block trades, at market prices prevailing at the time of sale or at negotiated prices, or as otherwise agreed with the applicable sales agent. This supplement shall be read in
conjunction with the prospectus supplement and the accompanying prospectus. Except as set forth herein, the prospectus supplement remains unchanged.
This supplement is being filed (i) to reflect the amendment dated on September 5, 2023, by and among the Sales Agents and us, or the
Amendment, of our sales agreement, dated May 13, 2020, as amended on February 26, 2021, March 1, 2022, February 22, 2023 and May 10, 2023, by and among us and the Sales Agents, or the Existing Sales Agreement, to reflect our
intention to revoke our REIT status, effective for our taxable year beginning January 1, 2024, subject to approval by our board of directors and (ii) to update certain related disclosure set forth under the heading U.S. Federal
Income Tax Considerations in the accompanying prospectus. Each reference to the term Sales Agreement in the prospectus supplement is hereby amended to refer to the Existing Sales Agreement as amended by the Amendment.
To assist us in qualifying as a REIT, among other purposes, stockholders are generally restricted from owning more than 9.8% in value or
number of shares, whichever is more restrictive, of the outstanding shares of our common stock, the outstanding shares of any class or series of our preferred stock, or the outstanding shares of our capital stock, and our charter contains certain
additional restrictions on ownership and transfer of our shares. As indicated in our Q2 2023 Form 10-Q, our management has made a determination that it would be advisable and in our best interests to revoke our REIT status, effective for our taxable
year beginning January 1, 2024, subject to approval by our board of directors. Pursuant to our charter, the restrictions on ownership and transfer of our stock will cease to apply, effective at the time as of which our board of directors determines
that it is no longer in our best interests to continue to qualify as a REIT. As a result, if our board of directors determines that, effective January 1, 2024, it will no longer be in our best interests to continue to qualify as a REIT, the
restrictions on ownership and transfer of our stock, including the 9.8% ownership limits, will terminate on January 1, 2024.