After three days of deliberations, the jury of six men and six women convicted Daudelin. He was charged with first-degree murder, sexual assault and forcible confinement.
Campeau disappeared while on her way to a friend's house in her Laval neighbourhood in 1995.
Police and neighbours scoured the woods near her house, and her body was found four days later.
Laval police concluded Campeau was murdered, but an arrest only came 16 years later — in 2011 — with the help of new DNA technology.
Throughout the trial, which wrapped up on Monday, the defence tried to sow doubt in the minds of jurors about the DNA evidence presented by the Crown and by the work of police officers. Police said they obtained a confession by getting Daudelin to believe he was recruited by a criminal organization and open up about his criminal past.
The Crown told jurors it had a solid case and said Daudelin revealed details about Campeau's murder to an undercover officer that only the killer could know.
A guilty verdict on a first-degree murder charge carries an automatic life sentence, without the possibility of parole for 25 years.