The 32-year-old Toronto man was on a Sunwing flight returning from Cuba when the incident took place just after midnight.
The plane landed safely and was taxiing towards its gate when the man opened an emergency exit and jumped, said Peel Regional Police, who were called to the scene.
"The door opened and somebody on the plane had to yell out that this gentleman had opened the door," said Const. Fiona Thivierge.
"Luckily, he was not injured."
Ground crews who were around the plane at the time held the man until police arrived, said Thivierge.
It was discovered the man had mental health issues and he was taken to a local hospital.
No charges have been laid.
"There's no criminality involved, it all comes under the Mental Health Act," said Thivierge, adding that this was the first such incident of its kind to her knowledge.