The Ontario Court of Appeal found the absence of aboriginals on the jury violated Clifford Kokopenace’s constitutional rights, and threw out his 2008 conviction.
The appeal justices ruled in a split decision last spring that the province had long known of the problem of aboriginal under-representation on juries but did little to address the issue.
In 2011, the Appeal Court upheld the manslaughter conviction as reasonable, but put the ruling on hold pending the outcome of the constitutional fight over the composition of the jury.
The years-long under-representation of aboriginals came to light at coroner's inquests in northern Ontario into the 2007 deaths of two aboriginals.
As usual, the Supreme Court gave no reasons Thursday for deciding to hear the case.
Kokopenace was convicted in 2008 of stabbing a friend to death on the Grassy Narrows reserve in northwestern Ontario.
In 2008, the jury roll for Kenora, where he was tried, comprised 699 potential jurors of whom only 29 or 4.1 per cent were on-reserve residents even though First Nation residents represented about 33 per cent of the district population.
"The integrity of the process was fundamentally compromised by the inattention paid by the state to a known and worsening problem, year after year,'' the appeal court said in its ruling.
"What the state knew or ought to have known was considerable; what the state did in response was very little."
Lawyer Julian Falconer, who speaks for the Nishnawbe Aski Nation which intervened in the appellate hearing, said the court laid out a standard of conduct for the Ontario government's dealings with First Nations in the context of the justice system.
"This case is of huge consequence because it leaves absolutely no doubt as to the extreme neglect on the part of the Ministry of the Attorney General as it relates to excluding First Nations from the jury rolls,'' Falconer said when the appeal ruling came down.