Republican senator Lisa Murkowski has joined the ranks of Rob Portman and Mark Kirk as the third Republican senator to publicly endorse same-sex marriage.

"I didn't just wake up and say, 'Oh my gosh, I'm going to do this'. No, it's something that I've been giving a lot of thought to over a long period of time," said the 56-year-old Alaskan senator, according to Politico.

In her op-ed piece posted to her official government website, Murkowski specifically named a lesbian couple as a major inspiration.

"The partners were two women who had first made the decision to open their home to provide foster care to the eldest child in 2007," she wrote.

"Yet despite signing up and volunteering to give themselves fully to these four adorable children, our government does not meet this family halfway and allow them to be legally recognized as spouses."

With the issue of gay marriage set to be ruled by the Supreme Court, the continuing shift in Republican leaders' public opinions on the matter could see a rising tide in favor of the issue.

"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."

Since her endorsement, the Human Rights Campaign has reportedly called the move "courageous and principled."

"As the Supreme Court prepares to rule in two landmark marriage cases this month, a growing bipartisan coalition is standing up for the right of all couples to marry, and there is no turning back that tide," noted HRC president Chad Griffin.

The Supreme Court is currently expected to deliver verdicts on the challenge to the Defense of Marriage Act and California's Proposition 8 either Thursday or the following Monday.

However, the decision could be delayed if they so choose.