Ontario’s top court has ruled that placing inmates in solitary confinement for more than 15 days constitutes cruel and unusual punishment, a resounding legal defeat of Correctional Service Canada’s long-standing practice of isolating prisoners for weeks, months and even years at a time.

The landmark decision sets a cap of 15 days on solitary placements, the first time a Canadian court has imposed a specific limit on solitary confinement. It would come into force by April 13, the court ruled, a tight deadline for an unwieldy government entity that oversees 43 prisons, 23,000 offenders and a $2.4-billion annual budget.

“With this decision, the Court of Appeal has brought to an end a sorry chapter in the administration of Canada’s prisons,” said Michael Rosenberg, who served as co-counsel on the case for the Canadian Civil Liberties Association (CCLA), which launched the challenge of solitary confinement four years ago. “This is a significant win for the CCLA and for the administration of justice more generally.”