A conservative U.S. senator who once opposed gay marriage is now supporting it after learning one of his sons is gay. The reversal makes him the only Republican in his chamber to back gay marriage as the high-profile issue faces comment soon from the country's highest court.

Sen. Rob Portman disclosed his change of heart in interviews with CNN and several Ohio newspapers. In an op-ed published Friday in The Columbus Dispatch, he said the decision came after a lot of thought.

"I have come to believe that if two people are prepared to make a lifetime commitment to love and care for each other in good times and in bad, the government shouldn't deny them the opportunity to get married," he wrote.

'Ultimately, for me, it came down to the Bible's overarching themes of love and compassion and my belief that we are all children of God.' —Sen. Rob Portman

Portman's reversal comes as the U.S. Supreme Court is expected to hear arguments this month in a challenge to a provision of the Defence of Marriage Act that denies equal benefits to gay couples.

As a member of the House of Representatives in 1996, Portman voted in favour of the Defence of Marriage Act, which defines marriage as between a man and a woman and bars federal recognition of same-sex marriage.

Since then, the issue of gay marriage has been taken up by individual states, and recent momentum has swung to approval of same-sex marriage despite conservatives' arguments that the act only should be between a man and a woman. President Barack Obama, a Democrat, has become more outspoken in his support for gay marriage after coming out on the issue during last year's presidential race.

Father wants his kids to be happy

Portman said his views on gay marriage began changing in 2011 when his son, Will, then a freshman at Yale University, told his parents he was gay and that it wasn't a choice but "part of who he was." Portman said he and his wife, Jane, were very surprised but also supportive.

He said it prompted him to reconsider gay marriage from a different perspective, that of a father who wants all three of his children to have happy lives with people they love.

Portman told reporters Thursday that his previous views on marriage were rooted in his Methodist faith.

"Ultimately, for me, it came down to the Bible's overarching themes of love and compassion and my belief that we are all children of God," he wrote.

The well-known Ohio conservative, a former U.S. trade representative and White House budget chief, was considered but not chosen as Republican presidential nominee Mitt Romney's running mate.

Portman told the newspapers Romney was informed about Will's sexuality last year.