Republican Sen. Lisa Murkowski of Alaska said Wednesday that she supports legalizing same-sex marriage, becoming the third GOP member of the Senate to endorse the right of gay and lesbian couples to marry.

Days before the Supreme Court is set to issue decisions regarding the Defense of Marriage Act and California’s ban on same-sex marriage, Murkowski joined Republican Sens. Rob Portman, Ohio, and Mark Kirk, Ill., in supporting same-sex marriage.

"I am a life-long Republican because I believe in promoting freedom and limiting the reach of government," Murkowski wrote in an op-ed explaining her decision. "When government does act, I believe it should encourage family values. I support the right of all Americans to marry the person they love and choose because I believe doing so promotes both values: it keeps politicians out of the most private and personal aspects of peoples’ lives – while also encouraging more families to form and more adults to make a lifetime commitment to one another."

The president of the Human Rights Campaign, a leading gay rights group, hailed the decision.

“We hope other fair-minded conservatives like Senator Murkowski stand up and join her,” HRC President Chad Griffin said in a statement. “Alaska may be nicknamed ‘the Last Frontier,’ but we’ve got to make sure that LGBT Alaskans don’t have to wait to find justice.”

Murkowski had previously said her views on same-sex marriage were “evolving,” using the language President Barack Obama had once used to describe his own views before endorsing marriage rights. She had been one of the few Republicans to support the repeal of “Don’t Ask, Don’t Tell.”

A veteran GOP senator, Murkowski has become somewhat unmoored from the rest of the Republican conference in the Senate following her re-election in 2010. After having lost the Republican nomination in Alaska to Tea Party favorite Joe Miller, Murkowski waged an unusual, independent write-in campaign, which she rode to re-election – a rare feat in politics. Since returning to the Senate, she has conferenced with the rest of the GOP.

Most other Republicans remain on record as opposing same-sex marriage, though activists who support same-sex marriage hope that the steady trickle of prominent Republicans who have endorsed the rights of gays and lesbians to marry may break the conservative logjam on the issue. An ABC News/Washington Post poll earlier this month found that 33 percent of Republicans support allowing gays to marry, while 65 percent of Republicans oppose it.

At the same time, activists have also ratcheted up pressure on high-profile Democrats – including a number of centrist senators – to endorse same-sex marriage.