The 23-year-old actress complemented her edgy, sophisticated look with smoky red eye make up and sleek, pulled-back hair.
According to the Daily Mail, the "Twilight" star arrived at the event with her designer, McCartney, and fellow actress Cameron Diaz.
McCartney also tweeted a photo of herself with Stewart wearing her creation before the event:
Theater accidentally screens 'Nymphomaniac' trailer instead of Disney's 'Frozen'
Britney Spears on kissing Ryan Gosling, Justin Timberlake in the Mickey Mouse Club