British-American director Christopher Nolan's film starred Irish actor Cillian Murphy as theoretical physicist J. Robert Oppenheimer, leader of the United States effort in the 1940s to create a weapon devastating enough to end World War 2.
Murphy won the best actor trophy, and Nolan was named best director at the awards on Sunday (local time) in Los Angeles.
A three-hour historical drama about science and politics, Oppenheimer became an unlikely box office hit and grossed $US953.8 million ($NZ1.53 trillion), in addition to widespread critical praise.
It was the first of Nolan's films to win best picture. The director has previously won acclaim for The Dark Knight Batman trilogy, Inception, Memento and other movies. He had been favoured to win the Oscar after earning best director awards at the Golden Globes, BAFTA, Critics Choice and the Directors Guild of America this year.
In his acceptance speech, he thanked Universal and its executive, Donna Langley, who made a big bet on the film, and also praised his cast and his family.
Nolan noted that movies are just a little bit over 100 years old and thanked the Academy for the honour.
"We don't know where this incredible journey is going from here. But to know that you think I am a meaningful part of it means the world to me."
Nolan also wrote the screenplay for Oppenheimer and produced the film with his wife Emma Thomas. The film received 13 Oscar nominations.
Oppenheimer triumphed over feminist doll adventure Barbie, a movie it had battled in a box office showdown dubbed "Barbenheimer." Other best picture contenders included The Holdovers, a dramedy set in a New England boarding school, and the Holocaust tale The Zone of Interest.
The win caps a successful awards season for Cillian Murphy, who also picked up a Golden Globe, a BAFTA and a Screen Actors Guild award for his performance. It was his first Oscar nomination.
"We made a film about the man who created the atomic bomb. For better or worse, we're all living in Robert Oppenheimer's world," Murphy said in his acceptance speech. "So I’d like to dedicate this to the peacemakers everywhere."
Murphy, 47, who lives in Ireland and keeps a low profile in Hollywood, had his biggest role to date playing a tortured, morally ambiguous Oppenheimer. He is also known for leading roles in films including 28 Days Later and crime show Peaky Blinders, and for appearances in other Christopher Nolan projects, including the Dark Knight Batman trilogy and Inception.
"I'd like to thank my terrible childhood and the Academy, in that order," he joked before he saluted his wife Susan, who he said found him as a "snarly rescue pet" and "loved him back to life."
Second Oscar for Stone
Emma Stone claimed her second Academy Award, winning the best actress trophy for her role as a woman revived from the dead in the dark comedy Poor Things.
An emotional and flustered Stone began her speech by explaining that her mint green strapless gown had just ripped in the back.
"My dress is broken. I think it happened during I'm Just Ken. I'm pretty sure," she joked, referring to Ryan Gosling's campy performance at the ceremony of the Oscar-nominated song from Barbie.
In the Frankenstein-inspired Poor Things, Stone played Bella Baxter, a woman who is reanimated after suicide by a mad scientist (Willem Dafoe). The movie chronicles Bella's dramatic self-discovery and liberation.
The 35-year-old scored her first Oscar for the 2016 musical La La Land.
An emotional Randolph took to the stage in a shimmering baby-blue dress, recounting how she started off as a singer until her mother persuaded her to go to the theatre department, promising there was something there for her.
“For so long I have always wanted to be different and now I realise I just needed to be myself, and I thank you for seeing me,” she said.
While this is the first Oscar for the black American actress, she has dominated the awards season with a Golden Globe, a Critics Choice Award, a BAFTA and a SAG award for her role as the cafeteria manager at the New England school.
The drama, directed by Alexander Payne and distributed by Focus Features, sees three people thrown together at Barton Academy during the Christmas holidays in 1970.
British Holocaust drama The Zone of Interest was named best international feature. Director Jonathan Glazer addressed the Israel-Gaza conflict in his acceptance speech.
"Right now we stand here as men who refute their Jewishness and the Holocaust being hijacked by an occupation which has led to conflict for so many innocent people. Whether the victims of October the 7th in Israel or the ongoing attack on Gaza. All the victims of this dehumanization. How do we resist?" he said to cheers and applause.
The Boy and the Heron, Japanese director Hayao Miyazaki's semi-autobiographical film about grief, was named best animated feature.
Winners were chosen by the roughly 10,500 members of the Academy of Motion Picture Arts & Sciences.
Host compliments, takes jabs at actors
Talk show host Jimmy Kimmel, hosting the show for the fourth time, opened the ceremony by complimenting, and taking jabs at, many of the nominees and their films.
The comedian praised Barbie, the pink-drenched doll adventure, for remaking a "plastic doll nobody even liked anymore" into a feminist icon.
Before the film, there was "a better chance of getting my wife to buy our daughter a pack of Marlboro Reds" than a Barbie, Kimmel said on the broadcast, which was shown live on the US ABC network.
Kimmel said many of this year's movies were too long, particularly Martin Scorsese's three-and-a-half epic Killer of the Flower Moon about the murders of members of the Osage Nation in 1920s Oklahoma.
"In the time it takes you to watch it, you could drive to Oklahoma and solve the murders," Kimmel joked.
As the stars celebrated, hundreds of pro-Palestinian protesters angered by the Israel-Gaza conflict shouted and slowed traffic in the streets surrounding the Dolby Theatre in Hollywood. "While you're watching, bombs are dropping," one sign read.
"The Oscars are happening down the road while people are being murdered, killed, bombed," said 38-year-old business owner Zinab Nassrou.
At the awards venue, a handful of celebrities, including Mahershala Ali and singer Billie Eilish, wore red pins calling for a ceasefire in Gaza.
Actor Mark Ruffalo praised the protesters as he entered the theatre and raised a clenched fist. "We need peace," he said.
Elsewhere on the carpet, stars strutted in strong silhouettes, sparkles and a splash of Barbie-inspired pink.
After 2023 was marred by actors and writers strikes, the scars gave Hollywood a chance to celebrate two global hits.
Oppenheimer and feminist doll adventure Barbie, another best picture nominee, brought in a combined $US2.4 billion ($NZ3.8 billion) in a summer box office battle dubbed "Barbenheimer."
