The soft green gown, which was first seen on the designer's fall 2016 runway, was covered in sequins, featured a high-neckline and cascading fringing.
Emma kept her makeup minimal with a touch of glitter on her eyelids and a soft pink lip and wore her hair in a chic side-swept up-do.
While her co-star Ryan Gosling wasn’t at the premiere, it didn’t stop her gushing about her ‘buddy’.
"It's wonderful to work with somebody you know, trust and respect so much. He's my buddy," she told Variety during the film’s press conference.
"I knew he could sing and dance. Once you've learned to ballroom dance with someone, you've learned everything you need to know," she added.
The film hits cinemas this December.