The actor, who played Michael Vaughn in the spy drama, announced his engagement to girlfriend Lauren Sklar last month.
Speaking to OK, he said: "She is my best friend in the world and that's why I asked her to marry me. I have more fun with her than anyone I've ever met.
"I knew pretty quickly. I'm 41 and I don't know if that has anything to do with it, but as you get older you know what you want and what you don't want."
He continued to say that the couple have already met with wedding planners but they will not be saying their vows until next year.
"She's basically going to have everything she wants. If she wants black tablecloths and a black gown I might have to put my foot down," he added. "But other than that I think it's her big day. It's my day too, but it's her big day."
Vartan currently appears in Hawthorne.