The Obama administration will recognise same-sex marriages performed in Utah and will provide federal benefits to the roughly 1,400 gay couples who were married there before the US Supreme Court halted such nuptials on Monday.
US Attorney General Eric Holder made the announcement this afternoon.
"These marriages will be recognised as lawful and considered eligible for all relevant federal benefits on the same terms as other same-sex marriages," Mr Holder said in a statement.
"These families should not be asked to endure uncertainty regarding their status as the litigation unfolds."
Utah's governor, Republican Gary Herbert, announced on Wednesday that the state would not recognise, at least for now, the marriages of gay couples who rushed to wed after a federal judge's ruling last month briefly allowed such marriages.
Utah temporarily became the 18th US state to legalise same-sex weddings when a federal judge ruled on 20 December that a state ban on gay marriage was unconstitutional.
The US Supreme Court on Monday put that lower-court ruling on hold at the request of officials in the conservative, predominantly Mormon state.
Gay rights advocates sent a letter to Mr Holder yesterday asking for federal recognition of those marriages that had been performed, and for the benefits such as tax breaks that go along with official legal status.
Federal recognition of the Utah gay marriages is consistent with a Supreme Court ruling in June that held that people in same-sex marriages are entitled to equal treatment under the law, Mr Holder said.
"This ruling [the high court's June decision] marked a historic step toward equality for all American families," Mr Holder said.
"And since the day it was handed down, the Department of Justice has been working tirelessly to implement it in both letter and spirit."
Little more than a decade ago, none of the 50 US states recognised same-sex marriage.
Since then, attitudes have changed rapidly in some parts of the country.