Const. Pascal Rossignol was on trial for 10 charges relating to alleged actions in Valleyfield, Que.
Cornwall police said the charges arose after an allegation was made to the force in October 2010, which it then referred to Ontario's Special Investigations Unit.
The SIU then determined the alleged offences happened in Quebec and an investigation was launched by that province's equivalent police watchdog run the Sûreté du Québec.
Cornwall police said the investigation then lasted two years before 10 charges were laid.
On May 28, Const. Rossignol pleaded guilty to three counts of sexual exploitation and two counts of procuring sexual services from a person under 18 years old.
Later that day, he also resigned from his position as a Cornwall police officer. He had been under paid suspension while awaiting trial.
Rossigno is scheduled for sentencing in a Valleyfield court on Sept. 17.