The British actor won the award for her lead role in the 2020 thriller-comedy film Promising Young Woman, in a ceremony that took place on Thursday 22 April.
During a touching acceptance speech, Mulligan said that McCrory “was a true independent spirit and actress” whom she has “looked up to and will continue to look up to” for the rest of her career.
She added: “Thank you for everything she gave us.”
Both actors have performed and found fame through London theatres in their respective careers.
McCrory died on 16 April after a “heroic battle” with cancer, her husband and fellow actor Damian Lewis said in a statement.
“I’m heartbroken to announce that after a heroic battle with cancer, the beautiful and mighty woman that is Helen McCrory has died peacefully at home surrounded by a wave of love from friends and family,” Lewis’s statement said.
“She died as she lived. Fearlessly. God, we love her and know how lucky we are to have had her in our lives. She blazed so brightly. Go now, little one, into the air, and thank you.”
Mulligan’s film Promising Young Woman is a tale of a woman who seeks to avenge the death of her best friend.
“I am shocked, amazed, and honoured to be a part of this group of amazing women,” said Mulligan, accepting the award at the virtual ceremony.
Mulligan also thanked the crew for surviving the 23-day shoot.
“They were painstakingly thought out and attentive and beautifully responsive to every scene. I’m so grateful to them, our cast, Margot Robbie, LuckyChap, Film Nation, and Focus Features,” she said.