"I am innocent and will appeal the decision," said Swaim, a 69-year-old director who has lived and worked in France since the late 1960s. He is best known for his 1982 film "La Balance".
The woman he was found guilty of assaulting was 22 at the time, and is also an US national.
She said during the trial that Swaim did not physically force her into a sexual relationship but explained she had "yielded to pressure" after a photo shoot at the director's Paris home in February 2007.
The woman told the court that she had trusted Swaim before the incident. "I really saw him like a father, as a paternal figure. It never even entered my head that he would be interested in someone like me."
She agreed that she had "embarked on something, over which [she] had no control."
Several friends of the young woman testified that she wasn't her usual cheerful self after the encounter, and her then-boyfriend told the court that she was suddenly very resistant to sexual relations with him.
Swaim, for his part, having initially denied that anything had happened, later said that the student had taken the initiative in the encounter.
He recounted the day in question for the court. "We were joking around, there was a certain atmosphere in the air. Then, she undid my fly, and performed fellatio on me. End of story," he said.
Swaim's lawyers attempted to undermine the credibility of the assault charges, pointing out that the victim had gone on to meet with Swaim several times after the incident, and that she had even taken part in another photo shoot with him.
Swaim, who was also fined €8,000 in damages on Thursday, has vowed to appeal the verdict.