The Supreme Court has upheld a dangerous offender law passed by the former Conservative government.

In an 8-1 ruling, the Supreme Court of Canada said the law passes constitutional muster because it maintains judges' discretion over whether an individual is declared a dangerous offender.

Under the law, judges are required to consider the treatment prospects of an offender before imposing a dangerous-offender designation, Justice Suzanne Côté wrote for the majority. Justice Andromache Karakatsanis dissented, saying the law has the potential to impose grossly disproportionate sentences on offenders.

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In 2008, the government of Stephen Harper rewrote the country's dangerous-offender law that had been previously been upheld by the Supreme Court. The new law changed how dangerous-offender hearings are conducted. And some judges interpreted the changes to mean they had no discretion at the first phase of the hearing – the designation phase, when they declare an individual a dangerous offender if they meet certain criteria for violence and recidivism.

The case involved Donald Boutilier, 47, of British Columbia. He pleaded guilty to six offences committed in 2010 in Vancouver, including a $300 robbery of a pharmacy, using an imitation firearm and leading police on a car chase. He also has a criminal record from the United States.

In a dangerous-offender hearing, a judge must decide what sentence the offender should receive: a fixed sentence, as in most criminal cases; a long-term supervision order of up to 10 years, after a jail term; or an indeterminate sentence. An indeterminate sentence means the court considers the offender beyond rehabilitating, and could be held for life. However, dangerous offenders who receive indeterminate sentences are still eligible for parole after seven years.

The trial judge who heard Mr. Boutilier's case declared him a dangerous offender, and sentenced him to an indeterminate sentence.

But the judge also declared part of the 2008 dangerous-offender law unconstitutional under Section 7 of the Charter of Rights and Freedoms, which protects life, liberty and security of the person. The judge said the law removes a judge's discretion at the "designation" phase of the process (where an offender may be labelled a dangerous offender), and that designation follows an offender for life, even if he receives a fixed sentence.

The B.C. Court of Appeal reversed that ruling, and said the law is a reasonable way of protecting public safety.

The Criminal Lawyers' Association intervened in the case to argue the law should be struck down. However, Catriona Verner, a lawyer representing the group, said Thursday there was much to like in the ruling.

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"In essence, they did what we were looking for, which is to give trial judges a lot of discretion before imposing an indeterminate sentence," for the purpose of ensuring that only a very small group of offenders receive such an extreme sentence.

An Indigenous group, Aboriginal Legal Services, intervened to argue the law should be declared unconstitutional because it has a harsh impact on Indigenous offenders; 31.5 per cent of dangerous offenders are aboriginal.