The 46-year-old, famously known for her role in Charlie's Angels, shared the news on Instagram on 27 August with a precious photo of her holding her son Rockwell Lloyd Liu.
Liu's rep confirmed to PEOPLE: "Rockwell Lloyd Liu was brought into the world via gestational carrier. Mum and baby are healthy and happy."
A "gestational surrogate" is when a surrogate is implanted with an embryo created by IVF, using the intended mother's egg and donor sperm.
Liu, currently starring in Elementary, captioned the snap: "Introducing the new little man in my life, my son Rockwell Lloyd Liu. In ❤️!"
She later posted a similar black and white snap of her and her son on Twitter, cradling him in an animal-printed blanket.
Although revealing the news via social media, the actress previously revealed she finds it hard to keep up.
She said, according to the Mirror: "'It's so hard to keep up with emails and lines and a 14-16 hour day of work. I'm not a daily Instagram or Twitter or Facebook person."
The actress is very private about her love life, but has most recently been linked to Israeli-American hedge fund billionaire Noam Gottesman according to People magazine.