And while Democrats in the Senate have supported the measure since it was proposed, it was only until after the midterms earlier this month that there were enough votes to surpass a probable filibuster -- a procedural motion that can stop bills in their tracks.
About 60 percent of Americans support a federal marriage equality law, according to a Politico and Morning Consult poll conducted last summer. Notably, the bill also protects interracial marriages.
The GOP lawmakers who voted in the affirmative were Sens. Susan Collins of Maine, Lisa Murkowski of Alaska, Rob Portman of Ohio, Mitt Romney of Utah, Thom Tillis of North Carolina, Roy Blunt of Missouri, Cynthia Lummis of Wyoming, Richard Burr of North Carolina, Shelley Moore Capito of West Virginia, Dan Sullivan of Alaska, Joni Ernst of Iowa, and Todd Young of Indiana.
Right before the vote on Tuesday, Collins said that the bill "will advance two goals: one, the goal of marriage equality for same-sex and interracial couples, and, second, the goal of strengthening religious liberty and conscience protections."
She also expressed her gratitude to her GOP colleagues for making the bill a bipartisan effort.
"I also want to thank all of the Republicans who have supported this," Collins said. "I know that it has not been easy, but they've done the right thing."
Here are the 12 Republican lawmakers who voted in support of the Respect for Marriage Act.