In Live By Night, she plays a sassy gangster's moll clad in the finest costumes from the 1920s and 1930s.
But Sienna Miller brought her wardrobe up to date as she walked the red carpet at the film's premiere in London on Wednesday, showing off her style queen status with aplomb.
The British actress appeared at the capital's BFI Southbank alongside her co-star Ben Affleck - also the film's writer, director and producer - fending off the chilly climate to wow in a strappy, slinky monochrome satin gown.
Sienna, 35, looked cool in the unique dress, which included a swathe of white silky fabric layered over a black underlay, giving the illusion of an undone nightie, pulled together with a large black flower.
It was a daring look and one that few could pull off with ease, but Sienna is one of those game few who can rock pretty much anything.
The fashionista - who opted for another daring, fashion-forward look at Sunday night's Golden Globes, a gorgeous cut-out white dress - finished her mid-week look with delicate curls in her hair and a rosy pink lip.
Ben, 44, looked dapper at the event in a slick blue suit, but the LA-based star was clearly not accustomed to London in January and opted for a thick coat to keep out the cold.
In Live By Night, Ben stars as Joe, a man who suffers deep emotional scars during the First World War and returns home to Boston where he begins life as an outlaw with friend Dion, played by Chris Messina.
Despite warnings from his police captain father, Joe begins a passionate affair with Emma Gould (Sienna), the mistress of an Irish mob boss.
Live By Night hits cinemas on January 13.