Since the inception of policing in Toronto, there has been a need to transport prisoners. Once arrested, a prisoner is taken to a police facility for investigation, then moved from jail to court and back as often as is necessary to resolve the case. Back in the early to mid 1800s, the arresting officer would have to hail a passing horse-drawn carriage to transport the suspect and himself to the police station. No formal "transport unit" existed until 1868. In that year, the Toronto Police Force bought a horse-drawn open-caged wagon. The cage allowed the public to see the person under arrest. Shortly thereafter however, this cage was converted to a solid steel box to prevent escape and protect prisoners who were occasionally injured by incensed citizens.

During the early years, the escorting constable was required to ride outside on the back step of the wagon. Escorting a violent prisoner was the exception to this rule. For some reason, it was felt it would be safer if the constable rode inside with them. This policy changed abruptly when an escorting officer was shot five times with his own revolver after being overpowered and disarmed by a prisoner. Fortunately, the officer survived.

In 1912, the TPF bought its first Motorized Patrol Wagon. It was quickly nicknamed the "Black Mariah" after similar black British vans. This wagon not only transported prisoners but it also doubled as an ambulance until 1920 when the city took over that responsibility.

By the 1930's, the force had increased its fleet of wagons, placing them at four separate stations around the city.

Transporting prisoners remained a police function until 1989. Increased calls for service and restrictive hiring budgets over the previous decade resulted in a general shortage of patrol officers.

In January 1989, prisoner transportation was civilianized. Court Services Security staff took over weekday transportation responsibilities, freeing police officers for regular patrol duties. Minimal weekend and evening prisoner movements were still handled by police officers.

In July of 1995, the Prisoner Transportation Unit officially began operating 24 hours a day, 7 days a week. Fifty-nine wagon officers, two dispatchers, five senior court officers, and one senior administrative court officer currently staff the unit.

The Prisoner Transportation Unit's 16 vans travelled 500,000 kilometres carrying 170,000 prisoners in 1999.