In 2011 Ergüven was invited to attend the Cannes Film Festivals Atelier to help develop her project, The Kings. While there she met fellow director Alice Winocour who was there to develop her first feature film Augustine. After Ergüven was unable to find financing for her film Winocour suggested she write a more intimate piece leading the two to begin work on the script for Mustang.
Her debut film Mustang premiered in the Directors' Fortnight section at the 2015 Cannes Film Festival where it won the Europa Cinemas Label Award. It later played in the Special Presentations section of the 2015 Toronto International Film Festival. The film was selected as the French entry for the Best Foreign Language Film at the 88th Academy Awards It was later shortlisted for the Academy Award for Best Foreign Language Film.
Ergüven was also nominated for multiple César Awards, winning the César Award for Best First Feature Film as well as the César Award for Best Original Screenplay.
Ergüven was the first person surprised by the film's overwhelmingly positive welcome. "During Cannes I was telling this joke: Tuesday we'll show the movie, Wednesday we'll talk to the press, Thursday we'll be old news. But that Thursday never came! We're still Wednesday and it's just getting more intense.", she says.
