The action will enable the government to extend eligibility for federal benefits to these couples. That means gay and lesbian couples can file federal taxes jointly, get Social Security benefits for spouses and request legal immigration status for partners.
Attorney General Eric Holder said the families should not be asked to endure uncertainty regarding their benefits while courts decide the issue of same-sex marriage in Utah.
The decision came days after Utah officials said they would not recognize the marriages. The office of Gov. Gary Herbert told state agencies this week to put a freeze on proceeding with any new benefits for the newly married gay and lesbian couples until the courts sort out the matter.
In a statement Friday afternoon, Herbert's office issued a statement that said Holder's announcement was unsurprising, but state officers should comply with federal law if they're providing federal services.
Attorney General Sean Reyes did not have an immediate comment on Holder's announcement.
More than 1,000 gay and lesbian couples took home marriage licenses from local clerks after a federal judge overturned Utah's same-sex marriage ban on Dec. 20. Utah voters approved the ban in 2004.
On Monday, the U.S. Supreme Court put a halt to same-sex marriages in Utah while the Denver-based 10th U.S. Circuit Court of Appeals considers the long-term question of whether gay couples have a right to marry in Utah.
State agencies aren't supposed to revoke anything already issued, such as a marriage certificate or a driver's license with a new name, but they are prohibited from approving any new marriages or benefits. State officials said the validity of the marriages will ultimately be decided by the appeals court.
Holder's declaration marked the latest chapter in the legal battle over same-sex marriage in Utah that has sent couples and state officials on a helter-skelter wave of emotions over the last three weeks.
Federal government agencies have previously confirmed that same-sex couples in other states are entitled to federal benefits, but this is the first time Holder has come out publicly and issued this kind of guidance, said Douglas NeJaime, a professor of law at the University of California, Irvine.
"Symbolically, it's an important step that the federal; government has taken," NeJaime said.
But it's not surprising, he said. The federal government has been making clear for several years that same-sex marriages should be honored.
"The fed government has been pushing up against the states that do not recognize same-sex marriages already," NeJaime said. "This is another step in that direction."
Holder said in a video on the Justice Department's website that the government will coordinate among agencies in the coming days to make sure Utah couples get the federal benefits they are entitled to.
The attorney general said that "for purposes of federal law, these marriages will be recognized as lawful and considered eligible for all relevant federal benefits on the same terms as other same-sex marriages."
Holder's declaration was greeted with applause among same-sex couples in Utah.
"It gives me hope moving forward in the appeals process," Moudi Sbeity said. "It shows that there really is a social and cultural shift in viewpoints and mindsets toward marriage equality."
Sbeity and partner Derek Kitchen are among three couples who brought the Utah lawsuit that led to the surprise Dec. 20 ruling by U.S. District Judge Robert Shelby, who said the state's ban on same-sex marriage violated gay and lesbian couples' constitutional rights.
Sbeity said he hopes Holder's declaration will persuade Herbert to shift the state's position. "I'm sure he doesn't want 1,300 lawsuits on his desk," Sbeity said.
Several hundred same-sex marriage supporters were planning a rally at the Utah State Capitol on Friday afternoon. Organizers planned to deliver a petition to the governor and state attorney general asking them to let the federal judge's ruling stand and allow gay marriages to continue.
Tim Wagner of Salt Lake City, one of the organizers of the rally said Holder's announcement was "pretty amazing" and a great thing for the newly married couples.
"It sounds like our national attorney general actually sees the law in the way it should be acknowledged," Wagner said. "The law is on the side of rights and the people who want to love the people they love."
On Thursday, the Utah attorney general issued legal advice to local clerks, advising them to finish paperwork for same-sex marriages completed before the Supreme Court issued a temporary halt.
Reyes' new advice was issued to clear up some confusion and only applies to marriages that were solemnized, said his spokeswoman, Missy Larsen.
"As long as the marital ceremony happened prior to the stay, then the marriage can receive documentation," Larsen said.
The attorney general's office said Thursday's guidance was not a decision on whether the marriages are valid.
Associated Press writer Michelle L. Price in Salt Lake City contributed to this report. Yost reported from Washington, D.C.