Sienna Miller with her new baby girl Marlowe Ottoline Layng in London on August 8, 2012. Credit:

Baby Marlowe is ready for the runway!

Sienna Miller stepped out for the first time with newborn daughter Marlowe on Wednesday.

The 30-year-old actress and fiance Tom Sturridge, 26, welcomed their baby girl one month ago in London. The British stars have been dating for over a year and Marlowe is the first child for each.

The first-time mom strolled the streets of London with Marlowe wrapped securely around her chest in a sling. Despite having only given birth last month, Miller (wearing no makeup) showed off her post-baby bod in tight jeggings and proudly revealed a makeup free face.

Showing a glimpse of her full head of brown hair, a sleepy baby Marlowe rubbed her eyes while enjoying the comfy stroll. Miller had a smile on her face as she held Marlowe and noshed on frozen yogurt.

Us Weekly chatted with the new mom last week via telephone at HBO"s Summer Television Association panel in Beverly Hills. "She's so cute," The Girl star, 30, gushed. "She's screaming upstairs. My brain doesn't work."

HBO's The Girl explores director Alfred Hitchcock (Tony Jones) and actres Tippi Hedren's (Miller) relationship with one another during the making of the 1963 classic The Birds.