VENICE — Alfonso Cuarón’s “ROMA” was awarded the Golden Lion for best film at the 75th Venice International Film Festival on Saturday by the competition jury led by Guillermo del Toro, last year’s winner of the top prize for “The Shape of Water.” Mr. Cuarón’s film, already considered a front-runner for the honor, follows the life of a housekeeper and the bourgeois family that employs her in the Mexico City of the 1970s.

Mr. Cuarón called the prize “a birthday present” to his family nanny, Libo, the model for the main character of “ROMA.” He singled out the film’s cast for praise “for portraying the women that raised me.”

The Silver Lion for best director went to Jacques Audiard for “The Sisters Brothers,” starring Joaquin Phoenix and John C. Reilly as two sibling assassins in the Old West. The Silver Lion Grand Jury prize was awarded to Yorgos Lanthimos for “The Favourite,” starring Olivia Colman as the mercurial monarch Queen Anne, opposite Rachel Weisz and Emma Stone as courtiers.

Ms. Colman also won the best actress award and critical praise for her role in the film, which was declared an “entertaining, mischievous, shrewd and archly feminist portrait of intrigue” by Screen Daily. Willem Dafoe received the best actor award for playing Vincent van Gogh in Julian Schnabel’s “At Eternity’s Gate.”