The Irish actress, 36, scooped the gong for Best Actress for her role in Chloe Zhao's Hamnet during this year's star-studded ceremony at the Royal Festival Hall.
One Battle After Another proved to be the big winner with six gongs, while Jessie Buckley won Best Actress, and Robert Aramayo earned a surprise honour for Best Actor for I Swear.
One was Ariana Grandewho was not named for her role in Wicked: For Good in the Best Supporting Actress category. Her co-star Cynthia Erivowas also not included for Best Actress.
Just hours before she was due on stage to accept the award for Best Actress at the Venice Film Festival, Nicole Kidman found out the devastating news that her mother Janelle had passed away.
Mikey, 25, triumphed over Demi, 62, Fernanda Torres, Karla Sofia Gascon, and Cynthia Erivo, to win the coveted gong for her starring performance in Anora.
Gascón had found herself in the crosshairs of controversy shortly after making history as the first openly-transgender actress nominated in the Best Actress category.
Demi's, 62, fury was palpable as the 25-year-old rising star's name was called out toward the end of the 97th Academy Awards - which featured a star-studded red carpet - in Hollywood on Sunday.