Nigel Adams, the Selby and Ainsty, said the 2013 law change has made a “positive difference for thousands of couples” around the country.
And the Goole-born politician added he would do things differently if possible.
He also joked people will appreciate how difficult it is for a “Yorkshireman to admit that they got anything wrong” as he backed moves to pardon gay men convicted of now abolished sexual offences.
Mr Adams, who is married to Claire, was speaking during the second reading of the Sexual Offences (Pardons Etc) Bill.
He said: “I would like to conclude my remarks by taking this opportunity to issue a mea culpa.
“During my first term in office I voted against equal marriage for a whole host of reasons.
“I thought at the time what I was doing was right but having now reflected and seen how that Act has made such a positive difference for thousands of couples around the country, I deeply regret that decision.
“I got it wrong.
“I can tell you, many in this House will know how difficult it is for a Yorkshireman to admit that they got anything wrong.
“So if I had the opportunity again, I’d vote differently.
“I want to apologise. I want to apologise to my friends, I want to apologise to family members and constituents who identify as gay, lesbian or bisexual.
“I want them to know that I believe in their full equality. I won’t have the chance to change that previous vote but I’m pleased to have the chance to stand in support of equality before the law today.”
SNP MPs applauded Mr Adams as he said he would back the Bill, moved by John Nicolson (East Dunbartonshire).