Posing alongside her co-star, Oscar nominee Chiwetel Ejiofor, Thandie wore a simple square-necked black dress with wide straps and an eye motif across the body.
The dress is from London-based fashion designer Osman.
The actress paired the outfit with metallic shoes and a satin navy blue clutch bag.
The pair were celebrating the premiere of their new film Half Of A Yellow Sun at the Odeon Streatham in London.
Chiwetel, who was nominated for his role in the Oscar winning film 12 Years A Slave, wore a smart black suit with a purple geometric tie.
The 41-year-old actress welcomed her third child on 3 March.
She tweeted the good news to her followers, posting: "Our baby boy is finally here! Booker Jombe Parker. Born joyously at home yesterday."
Thandie and Chiwetel at the premiere of Half of a Yellow Sun
Her spouse Ol Parker, a Hollywood screenwriter, also tweeted, telling his followers: "We had a baby, that's a beautiful thing. He's called Booker, and while he doesn't do much yet, I suspect him to be awesome."
"My 3rd home birth with brilliant independent midwife Caroline Flint - and Carole Goddard @PhoenixMidwives. Keep independent midwifery alive!" she added.
Their Twitter biography describes them as "a group of Independent Midwives who believe in a woman's ability to give birth naturally, given the right encouragement and support but minimum interference."
The couple already have two daughters, Ripley, born 2000 and Nico, born in 2004.