The Nazi satire "Jojo Rabbit" took home the best adapted screenplay honor.
The Writers Guild Awards were roughly a week before the Academy Awards, where both films will compete in the best picture category.
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The "Parasite" win went to Bong Joon Ho, who is also the film's director and Han Jin Won. Taika Waititi won for "Jojo Rabbit," a film he also directed and starred in.
HBO swept the top television awards, winning the drama category for "Succession," the comedy category for "Barry" and the best new series honor of "Watchmen."
The premium cable network's limited series also won the original long form prize, while FX's "Fosse/Verdon" won the adapted long form award.
Saturday's awards were handed out in concurrent ceremonies in New York and Beverly Hills, California.
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Don't miss the Oscars live on Sunday, Feb. 9, on ABC. Coverage begins at 4:30 ET | 3:30 CT | 1:30 PT on this ABC station.