The couple welcomed a baby boy, Atticus James, on Wednesday, Hewitt's rep confirmed to E!.
Their new bundle of joy joins big sister Autumn James, who the couple welcomed in November 2013.
The 36-year-old Criminal Minds actress announced in January that she was pregnant.
See Jennifer through the years:
Hewitt and Hallisay, 36, met on the set of The Client List, and began dating in 2012. The couple announced that they were both expecting and engaged in 2013, and tied the knot shortly before welcoming their first child.
Congrats to the happy couple!
Check out the video below for a look at some other celebrity baby bumps to keep an eye on this summer.