Photo

Senator Rob Portman, Republican of Ohio, has switched his stand on same-sex marriage, saying he now supports it after his son told him he is gay.

Mr. Portman, who had been considered one of the leading candidates to be Mitt Romney’s running mate in 2012, told Ohio newspapers that his son Will told him and his wife, Jane, in 2011 of his sexual orientation.

“It allowed me to think of this issue from a new perspective, and that’s of a dad who loves his son a lot and wants him to have the same opportunities that his brother and sister would have — to have a relationship like Jane and I have had for over 26 years,” Mr. Portman was quoted by Cleveland.com as telling reporters in an interview in his Washington office.

“If anything, I’m even more proud of the way he has handled the whole situation,” the senator said of his son, a student at Yale. “He’s an amazing young man.”

TimesCast Change of Heart The Times’s Jeremy W. Peters on Senator Rob Portman’s switch to support gay marriage.

His decision to become the only sitting Republican senator to so publicly embrace same-sex marriage comes after President Obama switched his position during the 2012 campaign to support such unions. The president announced his new position as Americans have been steadily shifting their attitudes on the issue, with polls showing an increasing numbers of Americans accepting gay marriages.

Mr. Portman said that when he was being considered for Mr. Romney’s ticket last year, he told the candidate that his son is gay.

While he was not selected as Mr. Romney’s running mate, the senator was a key adviser through his campaign, and played the role of President Obama as Mr. Romney prepared for the presidential debates.

Word of Mr. Portman’s switch on the issue came the same day that a fellow Republican senator, Marco Rubio of Florida, who is considered a likely 2016 presidential contender, appealed to conservatives by defending his stance on key social issues, including his opposition to same-sex marriage.

“Just because I believe states should have the right to define marriage in a traditional way does not make me a bigot,” he told the Conservative Political Action Conference on Thursday in a speech in Maryland.

Mr. Portman was a sponsor of the 1996 Defense of Marriage Act that is now being reviewed by the Supreme Court. He says now that states should be allowed to decide whether to allow same-sex marriage based on the will of voters.

Last month, dozens of prominent Republicans signed a legal brief stating their support for same-sex marriage, but no sitting Republican senators signed on.