In a video taped for the Human Rights Campaign, a national gay rights group, Bush calls on the legislature to legalize gay marriage, which it did not do when a bill was presented and defeated in Albany in 2009.
"I am Barbara Bush, and I am a New Yorker for marriage equality," she says in the clip. "New York is about fairness and equality. And everyone should have the right to marry the person that they love."
As the video concludes, Bush - who lives in Manhattan - urges other residents of the state to "join us."
The Human Rights Campaign plans to show the video at its annual gala in New York this weekend, according to the New York Times.
In an interview with the Times, Brian Ellner, who oversees the HRC's campaign for same-sex marriage in New York, said that a generational shift seemed to be aiding his organization's efforts.
"No matter what party they belong to, young Americans believe in basic fairness and equality," he said.
As president, George W. Bush advocated for the Federal Marriage Amendment - a proposed constitutional amendment that would limit marriage to heterosexual couples and ban civil unions and domestic partnerships.
But like Meghan McCain and Mary Cheney before her, Barbara Bush has now publicly embraced an issue that has become divisive in Republican circles and set several of the GOP's royal families at odds. While a presidential candidate in 2008, Sen. John McCain opposed gay marriage but both Meghan and her mother, Cindy, posed for the No H8 Campaign, a movement opposed to California's Proposition 8 which banned gay marriage in the state. Meghan and her father have also disagreed over the recently ended "don't ask don't tell" policy that prevented gay and lesbian members of the military from serving openly; she supported its repeal, while he did not.
Mary Cheney, the lesbian daughter of Vice-President Dick Cheney, is thought to have greatly influenced her father's thinking on the subject. He went from supporting the Bush administration's backing of the Federal Marriage Amendment to supporting gay marriage, provided it didn't run afoul of state and federal law.
And even George W. Bush's wife, Laura, has voiced her own support for same-sex marriage, saying in a May television interview that, "When couples are committed to each other and love each other," that they should have "the same sort of rights that everyone has."