Matthew Hiltzik, a friend of the couple, announced the Saturday nuptials in Manhattan on Twitter.
"Hilaria Thomas and Alec Baldwin were married this evening ... in New York City, sharing the occasion with family and friends inside the Cathedral, and Alec warmly receiving congratulations from well-wishing fans on his way into the service," he wrote.
Thomas, 28, wore a silk magnolia trumpet Amsale gown with cap sleeves and keyhole back neckline accented with crystal buttons, People magazine reported. Amsale also outfitted Thomas' mother and Baldwin's 16-year-old daughter Ireland Baldwin.
Baldwin, 54, wore a Tom Ford tuxedo.
The reception was at NYU's Kimmel Center, People reported.