Ashburn, who consistently voted against gay rights measures during his 14 years in statewide office, came out in an interview with KERN radio in Bakersfield, the area he represents.
Ashburn said he felt compelled to address rumors that he had visited a gay nightclub near the Capitol before his DUI arrest.
"I am gay ... those are the words that have been so difficult for me for so long," Ashburn told conservative talk show host Inga Barks.
The 55-year-old father of four said he had tried to keep his personal life separate from his professional life until his March 3 arrest.
"When I crossed the line and broke the law and put people at risk, that's different, and I do owe people an explanation," he said.
Ashburn was arrested after he was spotted driving erratically near the Capitol, according to the California Highway Patrol.
The next day, reports surfaced that he had left Faces, a gay nightclub, with an unidentified man in the passenger seat of his Senate-owned vehicle.
"The best way to handle that is to be truthful and to say to my constituents and all who care that I am gay," he said. "But I don't think it's something that has affected, nor will it affect, how I do my job."
Ashburn has voted against a number of gay rights measures, including efforts to expand anti-discrimination laws and recognize out-of-state gay marriages.
Last year, he opposed a bill to establish a day of recognition to honor slain gay rights activist Harvey Milk.
Equality California, a group that advocates for expanded gay rights and other issues, said it consistently gave Ashburn a 0 rating on its scorecard.
The senator said those votes reflected the way constituents in his district wanted him to vote.
Ashburn has been on personal leave since his arrest but was expected to return Monday to the Senate. His spokesman, Noel Libang, did not immediately return a call from The Associated Press seeking comment.
In the radio interview, Ashburn said he is drawing on his Christian faith, and he asked people to pray for him.
He said he does not plan to run for any public office after his term ends later this year.