The British actress, 41, made a stunning appearance at the Audi International at Guards Polo Club, near Windsor, to support England as they faced Argentina for the Coronation Cup.
Accompanied by actors such as Eddie Redmayne and Gemma Arterton, the star showed off her enviable physique in a short print dress and sky-high heels.
The star hasn't let her recent maternity affect her social life. Last week the Rogue star was also spotted at the Bella Freud Parfum fragrance launch.
Days before, she had taken her newborn son Booker to the Latitude Festival and shared a snap of the sweet moment with her Twitter followers.
Latitude Fest with baby Booker about to witness his namesake Booker T. Good times pic.twitter.com/fQKWD8s4Vy— Thandie Newton (@thandienewton) July 20, 2014
The star recently explained the reason behind her choice to have a home birth.
"He was born on the bathroom floor," she said on the TODAY show.
"I had just associated hospital with being ill, and I felt beautiful and healthy and wonderful when I was pregnant, and being at home is the place I felt most relaxed and comfortable," she said.
"So for me, it feels normal, but there was a time when everybody had their babies at home and it wasn't such a big deal".