Nomadland, Chloe Zhao's portrayal of communities who move around the American West, was named best feature, continuing its dominance of awards season at the Film Independent Spirit Awards.
The film also won prizes for its editing and cinematography, with the latter by Cornish cinematographer Joshua James Richards, while Zhao took home best director.
Nomadland has won best film at the Golden Globes, Baftas, Critics' Choice Awards and Producers Guild of America Awards, among others.
The Spirit Awards, where qualifying movies must have been made within a budget of $22.5m (€18.7m), Ahmed won best male lead for his portrayal of a punk rock drummer losing his hearing in Sound Of Metal.
The actress award went to Mulligan for her lead role in revenge thriller Promising Young Woman.
In her acceptance speech, Mulligan dedicated the prize to Peaky Blinders star Helen McCrory, who died last week aged 52 following a battle with cancer.
She said: "I want to dedicate this award to a true independent spirit, an actress that I have looked up to and will continue to look up to for the rest of my career, Helen McCrory.
"So thank you to her for everything she gave us."
Emerald Fennell won the prize for best screenplay for the Promising Young Woman, which was her directorial debut.
The Spirit Awards, an annual celebration of independent cinema, usually take place on the eve of the Oscars in a tent on the windswept beach at Santa Monica.
However, this year's virtual ceremony was held three days before Hollywood's biggest night and hosted by Saturday Night Live star Melissa Villasenor.
A-list presenters included Adam Sandler, Laura Dern, Cate Blanchett, Phoebe Waller-Bridge and Don Cheadle.
The first award of the night, best supporting female, went to Yuh-jung Youn, who has become used to delivering awards show acceptance speeches thanks to her portrayal of a wily grandmother in Minari.
The South Korean actress, 73, is widely tipped to win an Oscar on the weekend.
Her Spirit Awards acceptance speech was not as memorable as the one she delivered at the Baftas, where she called British people "snobbish".
During her recorded message at the Spirit Awards, she thanked her Minari "family" and reserved special praise for director Lee Isaac Chung, who she described as "my captain".
Veteran character actor Paul Raci won best supporting male for playing the boss of a shelter for deaf recovering addicts in Sound Of Metal.
Best documentary was won by Netflix's Crip Camp.
Andy Siara took home best first screenplay for time loop comedy Palm Springs while the director and producers behind Sound Of Mental won best first feature.
The Robert Altman Award, which honours an ensemble cast, director and casting director, went to the stars and creatives of One Night In Miami.
In the TV categories, Britain's Michaela Coel picked up the prize for best new scripted series for I May Destroy You, the acclaimed drama she created and starred in.
The show also won best ensemble cast.
Stars of TV drama Unorthodox celebrated a double victory. Shira Haas won best female performance in a scripted series while Amit Rahav was victorious in the male category.
List of all the winners
Best feature - Nomadland
Best director - Chloe Zhao (Nomadland)
Best male lead - Riz Ahmed (Sound Of Metal)
Best female lead - Carey Mulligan (Promising Young Woman)
Best supporting female - Yuh-jung Youn (Minari)
Best first screenplay - Andy Siara (Palm Springs)
Best first feature - Sound Of Metal
Best supporting male - Paul Raci (Sound Of Metal)
Best documentary - Crip Camp
Best screenplay - Emerald Fennell (Promising Young Woman)
Best editing - Chloe Zhao (Nomadland)
Best international film - Quo Vadis, Aida? (Bosnia)
Best cinematography - Joshua James Richards (Nomadland)
John Cassavetes Award - Residue
Best new scripted series - I May Destroy You
Best female performance in a scripted series - Shira Haas (Unorthodox)
Best male performance in a scripted series - Amit Rahav (Unorthodox)
Best new non-scripted or documentary series - Immigration Nation
Robert Altman Award - One Night In Miami 230551 APR 21
