The actress and her husband Laurence Fox reportedly welcomed their first child at the private Portland Hospital in London.
Chris Evans, Piper's ex-husband, visited the 26-year-old at the hospital and revealed: "Mum is very happy and I am really pleased. There are some tears of joy up there."
Piper began her career as a popstar before switching to acting. She has appeared in the BBC's Doctor Who revival and Secret Diary Of A Call Girl for ITV2.