The 72-year-old musician, who is already a father to seven kids, is excited to have a baby with Hamrick whom he's been dating for two years, reported Us Weekly.
"This is great news. It will be Mick's eighth child and nothing fazes him. He's been incredibly supportive," a source said.
This will be Hamrick's first child.
Prior to dating Hamrick, Jagger was married to Bianca Jagger and was in long-term relationships with Jerry Hall and late L'Wren Scott.
The Rolling Stones rocker is already father to seven children - daughters Karis, Jade, Elizabeth and Georgia, and sons James, Gabriel and Lucas - with the oldest kid being 45-year-old while the youngest is 17.
The pregnancy news comes just a little over a month after Jagger's bandmate Ronnie Wood welcomed twin girls with his wife, Sally.