LOS ANGELES — One of the most unpredictable awards seasons in memory took another small step toward clarity at Sunday evening’s SAG Awards, as Hollywood’s actors — who represent the motion picture academy’s largest branch — gave their highest honor to “Three Billboards Outside Ebbing, Missouri.”

Director Martin McDonagh’s dark morality tale took home three awards, including the top prize for ensemble, beating out “Lady Bird,” “Mudbound,” “Get Out” and “The Big Sick.” Frances McDormand won the lead actress award for her turn as a grieving mother who tries to spur the local police to solve her daughter’s murder, while Sam Rockwell earned the supporting actor award for his performance as a racist, dimwitted cop.

Though this year’s wide-open awards race has stymied even the most veteran Oscar prognosticators, the victories for “Three Billboards” — which follow its win earlier this month at the Golden Globes — could bode well for its Oscar prospects. Over the last 24 years, roughly half of the winners of the ensemble prize have gone on to win best picture at the Oscars.

That said, two of this year’s strongest contenders — Guillermo del Toro’s fantastical fable “The Shape of Water” and Steven Spielberg’s Pentagon Papers drama “The Post” — were left out of the SAG ensemble category.

Gary Oldman won the lead actor award for his acclaimed turn as Winston Churchill in the period drama “Darkest Hour.” Allison Janney earned the prize for her supporting turn as Olympic figure skater Tonya Harding’s mother in the dramedy “I, Tonya.”

On the TV side, NBC’s “This Is Us” won the award for ensemble in a drama series, with star Sterling K. Brown collecting the award for lead actor. HBO’s comedy “Veep” also won two awards for its ensemble and star Julia Louis-Dreyfus, as did its limited series “Big Little Lies,” which earned awards for Nicole Kidman and Alexander Skarsgard.

Coming in the midst of the industry’s ongoing sexual harassment scandals, the SAG Awards highlighted women throughout the ceremony, with a female host, actress Kristen Bell, and all-female awards presenters.

“Change is coming, and we are the agents of that change,” said SAG-AFTRA President Gabrielle Carteris. “We can and we must create an environment in which discrimination, harassment and abuse are no longer tolerated. Make no mistake, this is not a moment in time. This is a movement. And our strength comes in our unity.”