She confirmed her second pregnancy at the Chanel J12 cocktail party in Paris last month.
The actress, 34, donned a full-length floral dress infused with colours of pink, yellow and green underneath a light blue denim jacket as she stepped out in the capital.
Baby bump: Keira Knightley exuded a natural glow as she displayed her baby bump during a day out in London on Sunday
The Pirates of the Caribbean star paired her flowing dress with white laced sneakers as she stepped out for a stroll.
Letting her dark locks rest gently on her shoulders, the actress completed her look with a black handbag slung over her shoulders.