In a statement released immediately after the ruling, Boutonnat announced he was stepping down as head of the National Centre of Cinema (CNC), whose role includes overseeing measures to curb sexual violence in the industry.
The trial came as French cinema reels from a renewed #MeToo reckoning that has seen several big names, including acting legend Gerard Depardieu, accused of sexual abuse.
Seen as one of the most powerful men in French cinema, Boutonnat will be able to serve his one-year jail term at home wearing an electronic bracelet, said the Nanterre criminal court outside Paris.
Boutonnat, 54, was also banned from having any contact with the victim for three years.
In its verdict, the court ruled that the "plaintiff's version was more credible" than that of Boutonnat who, according to the court, had always exercised "a real influence" over his godson.
The court also found that Boutonnat's explanations "were not necessarily rational" and "could lead to confusion and imply" that of the two, he was "the one who had the greatest interest in keeping things quiet".
In the statement released by the CNC, Boutonnat "reaffirmed his innocence" and said he would appeal.
- 'More than godfather' -
Boutonnat's godson -- not a relative -- had accused him of trying to masturbate him during a holiday in Greece in 2020 when he was 19.
In court, the young man described Boutonnat as "more than a godfather.
"It's someone using me to masturbate," he said.
Boutonnat denied any sexual assault had taken place. He told the court that it was his godson who had initiated the situation and kissed him.
"I feel bad about leaving an ambiguous situation, but to say there was a sexual assault is false," he added.
During the hearing, Boutonnat was questioned about WhatsApp messages to his godson after the events, in which he said he had wanted to "challenge him on his sexuality".
Boutonnat was first appointed CNC chief in 2019. He was placed under investigation in February 2021 but still reappointed by the government as head of the CNC in July 2022.
In May, French Culture Minister Rachida Dati praised his work at the Cannes Film Festival.
"This case is a perfect demonstration of what sexual assault is," said the victim's lawyer, Caroline Toby, adding that "the abuse of authority" had been recognised in court.
On June 14, the prosecutor had requested a three-year suspended prison sentence for Boutonnat.
French cinema has been rocked by allegations that it has shrugged off sexism and sexual abuse for decades.
Training to prevent abuse has in recent months become obligatory for films seeking public funding via the CNC.
Numerous associations fighting against sexist and sexual violence in the film industry had denounced Boutonnat's leadership of the CNC.
The case was given renewed attention after actor Judith Godreche called for Boutonnat to be removed from his position during a landmark hearing in the upper-house Senate earlier this year.
CNC Deputy Director General, Olivier Henrard, will take over as interim head.
