The 39-year-old actor has been dating the Kissing Jessica Stein star since 1997, and although he calls her the "love of his life" he has no plans to exchange vows with the actress.
Hamm, whose divorced parents both died before he reached the age of 20, admits his troubled family life has played some part in his decision not to marry, but he's also convinced he's just not the 'marrying kind'.
He tells Parade magazine, "Losing both parents at a young age gave me a sense that you can't really control life - so you'd better live it while it's here. I stopped believing in a storybook existence a long time ago. All you can do is push in a direction and see what comes of it.
"I don't have the marriage chip, and neither of us have the greatest examples of marriages in our families. But Jen is the love of my life. We've been together four times longer than my parents were married (13 years)."
And Hamm reveals the couple isn't planning to start a family either, adding, "I like kids, but I also like the option to close the door. Becoming a parent is a whole other life, and it doesn't stop."