The Promising Young Woman star, 35, won the award for best female lead on Thursday night and dedicated her win to McCrory, who died last week at the age of 52.
"I just want to dedicate this award to a true independent spirit and actress that I have looked up to and will continue to look up to for the rest of my career: Helen McCrory," Mulligan said. "Thank you to her for everything she gave us."
Mulligan also paid tribute to her fellow nominees, saying, "I'm shocked and in awe and honored to be in this group of extraordinary women and I'm so floored by each and every one of their performances."
Mulligan was nominated alongside Viola Davis (Ma Rainey's Black Bottom), Frances McDormand (Nomadland), Nicole Beharie (Miss Juneteenth), Sidney Flanigan (Never Rarely Sometimes Always) and Julia Garner (The Assistant).
Rich Fury/Getty Images
She continued, "I need to just thank first and foremost Emerald Fennell for her complete genius in writing and directing and producing this work."
During her speech, Mulligan also thanked the cast, and credited the independent film crew who worked on the movie for being "painstakingly thoughtful and careful and beautifully sensitive."
Never miss a story — sign up for PEOPLE's free daily newsletter to stay up-to-date on the best of what PEOPLE has to offer, from juicy celebrity news to compelling human interest stories.
McCrory's husband, Billions star Damian Lewis, revealed the British actress had died on April 16 after a battle with cancer.
The actress is best known for her roles as Polly Gray in Peaky Blinders and Narcissa Malfoy in the Harry Potter films.
Promising Young Woman follows the wickedly smart and cunning Cassie (Mulligan) as she tries to avenge her best friend, who was sexually assaulted and murdered. The film is up for five Oscars, including Best Picture.