Ken Mehlman, President George W. Bush’s campaign manager in 2004 and a former chairman of the Republican National Committee, has revealed that he is gay and is working to advance the cause of same-sex marriage.

He confided his sexual orientation to family and friends in the last few months, he said in an interview Wednesday. He said it was a realization that he had come to over time. “At least for me, it wasn’t like there was a light-bulb moment,” said Mr. Mehlman, who is now a partner and head of global public affairs for Kohlberg Kravis Roberts, a private equity firm. “The reality is, it’s taken me 43 years to come to terms with this part of my life.”

The news was reported Wednesday by Marc Ambinder, a blogger for The Atlantic. There had been speculation about his sexuality, but Mr. Mehlman had in the past denied that he was gay.