The British star beat The Wife's Glenn Close to the top prize in a category that also included Lady Gaga (A Star is Born), Yalitza Aparicio (Roma) and Can You Ever Forgive Me? star Melissa McCarthy.
She was praised for her speech, which many have deemed the best of the night. You can read it in full here.
Earlier in the evening, Rami Malek took home Best Actor for his portrayal of Freddie Mercury in Queen biopic Bohemian Rhapsody. Mahershala Ali won Best Supporting Actor for this year's Best Picture winner, Green Book, while Regina King won Best Supporting Actress for her performance in If Beale Street Could Talk.
Winners at this year's ceremony included Olivia Colman for The Favourite, Rami Malek for Bohemian Rhapsody, Regina King for If Beale Street Could Talk and Mahershala Ali whose film Green Book won Best Picture. Alfonso Cuarón took home Best Director for his Netflix drama Roma.
You can find a full list of winners here.
Marvel blockbuster Black Panther made history as Ruth Carter and Hannah Beachler became the first black winners in the category of Best Costume Design and Best Production Design, respectively.
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