"The couple, who had been engaged for over a year, had been planning a formal wedding date, but Mr. Dillon’s schedule with Poseidon and Entourage had made it difficult," Dillon's spokesperson, Tiffany Kuzon, said in a statement.
"Entourage castmates Jerry Ferrara and Kevin Connolly were present at the ceremony."
Kuzon also said that the couple are expecting their first child this summer.
In HBO's hit comedy Entourage, which begins its new season in June, Dillon plays an obscure actor whose brother is an A-list celebrity – a role that spoofs his real-life relationship with older brother Matt.
Next month, Dillon will be seen in Poseidon, next month's big-screen remake of the ocean-disaster classic The Poseidon Adventure. He has also acted in the movie Platoon and on the TV shows 24 and NYPD Blue.