The couple, who were married in June 2013, named their son Jaxon Wyatt, according to Cavallari's Instagram account. The newborn weighed in at 7 lbs. 11 oz.
This is the second son for Cutler, 31, and the former Laguna Beach star. Their 20-month-old son, Camden, now has a baby brother.
"I'm lucky," Cavallari told E! News last year. "Both pregnancies have been really easy for me, I've just been really tired. It's just one of those things where I could literally sleep all day everyday but I'm snapping out of it a little bit now that I'm in the second trimester."
Cavallari didn't know the sex of her baby at the time of the E! News interview and said she'd be pleased either way. "I honestly don't care, I mean there's great things about both. Another boy would be fun, Cam would have a little buddy and then I'd be the woman of the house...but of course I want a little girl, so I don't know."
In November, Cavallari told CBS News her husband has been an "incredibly hands-on" dad. "He goofs around with Cam and he gets on the floor and plays with him. It's really cute to see."
Like most pregnant women, Cavallari marked her progress on Instagram:
And here's what Cavallari looked like the day before her son son was born.
Yea, not fair!
Congratulations to Kristin, Jay and Camden!
Image via YouTube