By Meghan Blalock
Dec 28, 2012 @ 9:00 am

Sienna Miller turns 31 today! The actress had a big year in 2012, with giving birth to daughter Marlowe in July, making a very strong case for the cape dress in October, and popping up regularly on InStyle's Look of the Day roster. Celebrate her big day by seeing how she transformed over the course of her career in the gallery!

MORE:• Sienna Makes a Case for the Cape• Sienna Miller’s Post-Baby Fashion Tips• Miller Welcomes a Baby Girl!