The 35-year-old and Platt welcomed son Jack on Saturday, Faris' representative confirmed, reported Us magazine.
"Anna Faris and Chris Pratt are happy to announce the birth of their beautiful baby boy Jack. He arrived earlier than expected and will be spending some time in the NICU.
"The happy parents thank you for your warm wishes and ask that you honor their privacy during this time," the representative said.
The actress announced in May she was expecting her first child with her "Moneyball" star husband, who she wed in 2009 in Bali.