Gilbert Rozon, who founded the Just for Laughs comedy festival, had always maintained his innocence.
The judge in Montreal said her ruling did not mean that no crime had taken place, but rather that the prosecution had not been able to prove Mr Rozon’s guilt beyond all reasonable doubt.
The complainant said the decision marked a “sombre day”.
Mr Rozon stepped back from several television productions in 2017 after a Montreal newspaper published allegations of sexual abuse and harassment from nine women spanning three decades. None of the claims have been proven in court.
The case centred on events in 1980, when Annick Charette – then aged 20 – accused Mr Rozon of raping her at a ski resort outside Montreal.
He denied the charges and said Ms Charette had initiated the encounter.
In her 30-page ruling, Judge Mélanie Hébert said Ms Charette’s testimony had been credible, but added that the verdict showed “that there remains, in the mind of the court, a reasonable doubt about the guilt of Mr Rozon, because the prosecution has not discharged its burden”.
The judge also praised the courage of the complainant, who waived her right to anonymity on Tuesday.
“To all the victims, I would like to tell you this: ‘Do not be ashamed,'” Ms Charette said after the decision was announced.
Mr Rozon, 66, is famous in both his home country of Canada and abroad. He founded the Just for Laughs festival in Montreal in 1983 and expanded the brand to include television shows and specials.
He also appeared as a judge on the French version of America’s Got Talent.
But allegations of sexual misconduct have swirled around him for more than a decade. He pleaded guilty to the sexual assault of a 19-year-old woman in 1998, which resulted in an absolute discharge. This is an option open to judges in Canada which means the guilty individual is immediately discharged with no conditions and no punishment is imposed.