The former The Hills and Laguna Beach star welcomed a son with her husband William Tell on July 5, Us Weekly reported.
Lauren posted about the arrival of her baby boy on Instagram late Wednesday night.
"He's here! We're so excited to welcome Liam James Tell into the world!" the 31-year-old fashion icon captioned a photo of a cross stitch depicting her immediate family, which includes two dogs.
Lauren revealed on New Year's Day that she and William, 37, were expecting their first child together. She shared a picture of her sonogram on Instagram that day and said she had "a feeling" 2017 would be "the best year yet."
And on May 20, Lauren's friends and family threw her a beautiful baby shower.
Lauren got pregnant a little over two years after tying the knot with William in a wedding on the California coast.
The former reality TV star and William, a graduate of the University of Southern California law school, wed in September 2014. The pair got engaged in October 2013 and began dating on Valentine's Day 2012.
However, Lauren laid eyes on the father of her baby way before they sparked up a romance.
"I met my husband when I was 16 and sitting on stage at one of his concerts," Lauren recently blogged of William, who was in the band Something Corporate from 2001 to 2004. "Ten years later, we were set up on a blind date."
Lauren left The Hills -- which MTV ended after six seasons in 2010 -- during its fifth season in 2009, ending a five-year period in which she starred on both The Hills and its Laguna Beach predecessor, which followed her as a 17-year-old high school senior in Laguna Beach, CA.