The Washington National Cathedral is a focal point of Christian worship in the United States. It has said that effective immediately, it will officiate same-sex weddings.
In a statement, its dean, Gary Hall, said the cathedral -- one of the biggest in the nation -- would marry gay and lesbian couples using a rite adapted from the Episcopal church's existing blessing ceremony.
"We enthusiastically affirm each person as a beloved child of God, and doing so means including the full participation of gays and lesbians in the life of this spiritual home for the nation," he said.
Same-sex marriage is legal in nine US states and the District of Columbia, but banned in around 30 other states. Later this year, the US Supreme Court is to consider the federal government's refusal to recognize LGBT marriages.
President Barack Obama, who last year became the first serving president to openly support marriage equality, is to attend a national prayer service at the cathedral on January 22 as part of the inauguration of his second term.