O'Hare revealed on Twitter that he and Redwood tied the knot at a New York City courthouse on Thursday.
The star wrote: "Okay. It happened. Hugo and I just got married."
Redwood and O'Hare were wed just four days after New York began to officially license same-sex marriages on July 24.
Governor Andrew Cuomo signed the state's Marriage Equality Act in June, making New York the sixth state to allow gay and lesbian couples to marry.
True Blood airs Sundays on HBO.
> True Blood Sam Trammell: 'Genre shows don't win Emmys'
> True Blood Kristin Bauer: 'Vampires try to rein Pam in'