Kicking her day off at the Up2Us gala, Sienna looked fresh as a daisy in a Burberry white cotton dress with cut-out eyelet detailing. Keeping the springtime look simple, Sienna styled her look with nude Prada pumps, Edeler earrings and twisted her hair up with minimal make-up for pared-down perfection.
The actress then amped things up for the evening, slipping into something that little bit more sultry for the premiere of her upcoming film, Just Like a Woman. Working another Burberry number, Sienna's ensemble was simple but sizzling as she showed off her black column dress.
The night-time transition was perfected by swapping flats for sky high black heels and loading lids with lashings of kohl for a hot high impact make-up look.
The perfect model for day to night dressing - which of Sienna's looks do you prefer? Let us know on Twitter.
WATCH: SIENNA MILLER TALKS FASHION AND STYLE WITH INSTYLE AND PIAGET