Comedy-drama Eighth Grade won the outstanding original screenplay prize at the Writers Guild Of America Awards.
In a shock result, writer Bo Burnham won ahead of heavyweights including Roma, Vice, Green Book and A Quiet Place.
The WGA Awards – one of the final ceremonies before Hollywood caps the year in film at the Oscars next week – honour the best in movie and TV writing over the previous 12 months.
Eighth Grade stars 15-year-old Elsie Fisher as a school girl struggling with social anxiety.
Accepting the marquee prize of the night in Los Angeles, Burnham said: “This all belongs to Elsie Fisher who performed the script. No one would care about the script if she hadn’t done it. I joined the guild when I was 18 and my mother did the paperwork, so thank you for that — and my father who did nothing.”
The other big award of the night, outstanding adapted screenplay, is between BlacKkKlansman, Can You Ever Forgive Me?, If Beale Street Could Talk, A Star Is Born and Black Panther.
The awards show carried a more irreverent tone than the more established ceremonies, with host for the evening Chelsea Peretti opening with a string of close-to-the-bone jokes.
The Brooklyn Nine Nine star warned the audience winners making long-winded speeches would be dragged off stage by FBI agents spying on a “room full of liberals”, adding: “Either that will happen, or your next project will be directed by Bryan Singer.”
Singer, the listed director on Queen biopic Bohemian Rhapsody, has been accused of sexual assault, which he denies.
Peretti also took aim at Bradley Cooper, poking fun at the director for his comments about dreaming of A Star Is Born before filming it.
The film is a remake, with previous incarnations arriving in 1937, 1954 and 1976.
Peretti said: “There could be 100 remakes of A Star Is Born in the room, and Bradley will still think he’s the only person who’s thought about it.”
However, the tone took a strikingly more sombre tone when Adam McKay took to the stage and called for people to remember the victims of the Iraq War.
Vice writer and director McKay was honoured with the Paul Selvin Award, which is handed out each year to the writer “whose script best embodies the spirit of the constitutional and civil rights and liberties which are indispensable to the survival of free writers everywhere”.
Taking to the stage, McKay said while making Vice, he felt a “responsibility every day” to tell the story of former US vice president Dick Cheney.
Cheney was a key figure in the US’s foreign policy in the wake of 9/11. McKay said the victims of the Iraq war need to be remembered and warned against forgetting about the George Bush presidency to focus on “what an orange goon Trump is”.
He added: “Don’t get me wrong, he is an orange goon.”
In the television categories, The Marvellous Mrs Maisel won outstanding comedy series and best episodic drama went to Homeland for the episode Paean To The People.
Best animation went to The Simpsons.
The Paddy Chayefsky Laurel Award, a prize handed out for an outstanding achievement in TV writing, was awarded to Jenji Kohan, for her work on shows including Weeds, Orange Is The New Black and Glow.