Moore beat Felicity Jones ("The Theory of Everyting"), Marion Cotillard ("Two Days, One Night"), Reese Witherspoon ("Wild") and Rosamund Pike ("Gone Girl) for the award. She has been nominated five times and is one of 11 actors nominated for two Oscars in the same year (in 2003, for "Far From Heaven" and "The Hours"). This is Moore's first Academy Award.
"There's no such thing as Best Actress, as is evidenced by the performance of the nominees," the actress said when she took the stage. Moore also said she was grateful that "Still Alice" helped shine a light on Alzheimer's disease. "People with Alzheimer's deserve to be seen so we can find a cure."
In "Still Alice," which is based on Lisa Genova's 2007 novel by the same name, Moore plays Alice Howland, a Columbia University linguistics professor diagnosed with early onset Alzheimer's disease. Moore told HuffPost Entertainment last month that the film gave her a deeper appreciation for everything in her own life. "I think really what the movie does is make you think about what you care about and what you want in your life and not taking anything for granted," she said.
Moore's win came as no surprise, as she's been sweeping the awards circuit this year. For "Still Alice," Moore also won the Golden Globe for Best Actress - Drama, as well as the Screen Actor's Guild Award, the BAFTA and the Critics' Choice Award, among others.
Last year, Cate Blanchett won Best Actress for her role in "Blue Jasmine."
For a full list of Oscar winners, head here.