"Introducing the new little man in my life, my son Rockwell Lloyd Liu. In [love]," she wrote next to a picture holding her little man.
The 46-year-old, who has never been married, had her son "via gestational carrier. Mom and baby are healthy and happy," her rep confirmed to ABC News.
Liu has been starring on the hit show "Elementary" since 2012 and is set to be featured in "Kung Fu Panda 3" next year.
She is also a UNICEF ambassador since 2004 and "has involved herself in almost all aspects of UNICEF's various campaigns and initiatives and has been influential in supporting its mission of saving and improving children’s lives worldwide," the organization's website reads.