While accepting her prize the star was unexpectedly interrupted by her husband, John Krasinski, who rushed on stage to congratulate her.
Emily was honoured for her role in Edge of Tomorrow, in which she stars as Sergeant Rita Vrataski.
As the 31-year-old began her acceptance speech, John rushed up behind her and lovingly planted a kiss on his wife.
Turning to the crowd, Emily explained the The Office US star – with who she welcomed daughter Hazel last February – was already waiting in the wings. "He's presenting next!" she said.
And later added: "To my sneaky husband, John Krasinski, for being okay with the fact that he was married to a veiny, sinewy wrestler for the duration of this film, and also coming up with my favourite line ever which was, 'I'm terrified I'm gonna wake up one morning and you're benching me.'
"Which I did, just to kind of freak him out."Â
Emily was the only British winner of the night.Â
Other nominees included Rosamund Pike and Felicity Jones for their roles in Gone Girl and The Theory of Everything, respectively.Â
The starlets were competing in the Best Actress category, but they lost out to Julianne Moore for her stand out role in Still Alice.
Keira Knightley was also up for was up Best Supporting Actress, playing Joan Clarke in The Imitation Game.
The pregnant star lost out to Boyhood actress Patricia Arquette.Â
Benedict Cumberbatch, Eddie Redmayne and Ralph Fiennes battled it out in the Best Actor category, but the coveted prize was clinched by Birdman star Michael Keaton.