The Episcopal Church is a small but highly prominent part of American Christianity The church has long been supportive of equality for gay men and lesbians.
"It's something for us to say we are going to do this in this very visible space where we pray for the president and where we bury leaders," the Reverend Gary Hall, who became dean of Washington National Cathedral, says. "This national spiritual space is now a place where [lesbian, gay, bisexual and transgender] people can come and get married."
The vast majority of houses of worship don't host blessings or weddings for people of the same gender.
The Episcopal Church, with two million members, has been something of an exception. Dozens of parishes have broken with the denomination over the issue.
The Washington diocese, which includes the District and the Maryland suburbs, has more than 80 parishes, most of which host same-sex blessings.
Longtime observers estimated that more than half of parishes across the denomination host the blessings.
Episcopal clergy in Washington have been overseeing blessings for commitment ceremonies for same-sex couples since about the 1980s.
In addition, the church has approved a rite for same-sex blessings. Previously, clergy adapted the rite used for heterosexual couples.
The "heterosexual marriage [ritual] still has some vestiges of patriarchy, with woman being property. There's hope in same-sex marriage that it is a teachable moment for heterosexual couples. The new rite is grounded in baptism and radical equality of all people before God," Hall says.
"I'd like to use it for heterosexual weddings because I think it's so much better than our marriage services."
David Masci, a senior researcher at the Pew Forum who has focused on the issue of same-sex marriage and religion, notes that the larger U.S. faith communities, such as the Catholic Church, the Southern Baptist Convention and most of the nondenominational Christian world - "aren't even considering these sorts of things."
Masci notes that younger evangelicals generally seem more open on the topic of homosexuality than middle-aged or older ones.