The long-term couple, who have been engaged for four years, married at the Beverly Hills County Clerk office in Los Angeles.
According to TMZ, the two lovebirds intended to get their marriage license but once they were there, decided to tie the knot in that very moment.
Kristen, 33, and Dax, 38, who have a six-month-old daughter called Lincoln together, had abstained from marriage until now for political reasons.
While they had discussed marriage – Dax referred to the House of Lies actress as his wife even before the two tied the knot – they openly spoke about their decision not to wed until gay marriage had been made legal in their home state of California, out of respect for their friends.
"The reason we're not rushing to get married is because I don't feel appropriate taking advantage of a right that's denied my (gay and lesbian) friends," Kristen told the Advocate in August of last year.
It was a sentiment echoed by Dax when he spoke to CNN in 2012. "We're not punishing America by not getting married…" he said.
"We're not going to have a party and invite all our friends, half of whom can't (get married). We're not going to ask them to come and celebrate a right they don't have. That's just tacky."
When California's ban against gay marriage was overturned in June, Kristen celebrated by tweeting Dax – who was already her fiancé - "@daxshepard1 will you marry me? Xo #marriageequality #loveislove."