The Human Rights Campaign, a national gay rights organization, released a video Tuesday featuring the 29-year old Bush, a New York resident who runs Global Health Corps, a nonprofit public health organization.
"I'm a New Yorker for marriage equality," Bush says in the video. "New York is about fairness and equality and everyone should have the right to marry the person that they love."
Paul Guequierre, a spokesman for the Human Rights Campaign, said the video was produced to help promote efforts to win same-sex marriage rights in New York. A bill legalizing gay marriage passed the New York state Assembly in 2009 but was defeated in the state Senate that year. But Gov. Andrew Cuomo, a Democrat, has announced his support for same-sex marriage, and advocates believe they have enough votes in both chambers for a bill to pass this year.
"New York is one of our priority states," Guequierre said.
Barbara Bush's advocacy for gay marriage is a sharp departure from her father's position on the issue.
The former president was an opponent of same-sex marriage and in 2004 announced his support for a proposed constitutional amendment to outlaw it. But his wife, former first lady Laura Bush, has said she supports gay marriage as does former Vice President Dick Cheney, whose daughter Mary is gay.
Spokesman David Sherzer said the former president had no comment on his daughter's video.
Advocates say they approached Bush to appear in the video after she attended a fundraiser for the American Foundation for Equal Rights, an organization created to challenge California's Proposition 8, a 2008 ballot initiative that struck down gay marriage in that state. The group was founded by attorney Ted Olson, a prominent Republican who with Democratic attorney David Boies challenged Proposition 8 in federal court.
Barbara Bush's twin sister, Jenna Bush Hager, has not indicated her position on gay marriage.