Kagan presided on Sunday over the wedding of former clerk Mitchell Reich and Patrick Pearsall in the Washington suburb of Chevy Chase, Maryland.
Supreme Court spokeswoman Kathy Arberg said Monday that the same-sex ceremony was the first at which Kagan officiated.
Retired Justice Sandra Day O'Connor and Justice Ruth Bader Ginsburg have previously officiated at the wedding of gay and lesbian couples, including at the Supreme Court. Ginsburg most recently performed the wedding of Washington theatre director Molly Smith.
The court could decide in its upcoming term whether same-sex couples nationwide have the right to marry under the Constitution.