“Joker,” directed by Todd Phillips, was awarded the Golden Lion for best film at the 76th Venice International Film Festival on Saturday by a competition jury led by the Argentine filmmaker Lucrecia Martel. The film received fervent attention as well as critical praise for its portrayal of its troubled, murderous central figure, drawn from the DC Comics character and played by Joaquin Phoenix.

“There is no movie without Joaquin Phoenix, the fiercest and bravest and most open-minded lion that I know,” Mr. Phillips said in an acceptance speech, playing on the name of the festival’s signature awards. The director also thanked the film’s studio, Warner Brothers, and DC Comics for “stepping out of their comfort zone” and “taking such a bold swing on me and this movie.” Mr. Phillips’s previous films include comedies such as “The Hangover,” its two sequels and “Old School.”

The award for “Joker,” an unusual selection for the Venice competition, came on the heels of an unexpected high-profile honor for a new film by Roman Polanski. The Silver Lion, the penultimate prize, went to Mr. Polanski’s “An Officer and a Spy,” a retelling of the anti-Semitic persecution of the French army officer Alfred Dreyfus.

Mr. Polanski, who fled the United States four decades ago while awaiting sentencing for statutory rape, remains a flash point for controversy and was expelled from the Academy of Motion Picture Arts and Sciences in 2018. The French actress Emmanuelle Seigner, who is married to Mr. Polanski and in his new film, accepted the award on his behalf. Mr. Polanski did not attend the festival.