Supreme Court Chief Justice Beverley McLachlin says Canada attempted to commit "cultural genocide" against aboriginal peoples, in what she calls the worst stain on Canada's human-rights record.

Genocide – an attempt to destroy a people, in whole or part – is a crime under international law. The United Nations' Convention on the Prevention and Punishment of the Crime of Genocide, adopted in 1948, does not use the phrase "cultural genocide," but says genocide may include causing serious mental harm to a group.

Chief Justice McLachlin appears to be the highest-ranking Canadian official to use the phrase. Former Liberal prime minister Paul Martin used it two years ago in describing residential schools for aboriginal children when he testified before the Truth and Reconciliation Commission set up by the Conservative government. That commission is to make its report public next week.

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"The most glaring blemish on the Canadian historic record relates to our treatment of the First Nations that lived here at the time of colonization," Chief Justice McLachlin said. She was delivering the fourth annual Pluralism Lecture of the Global Centre for Pluralism, founded in 2006 by the Aga Khan, spiritual leader of Ismaili Muslims, and the federal government.

After an initial period of inter-reliance and equality, she said Canada developed an "ethos of exclusion and cultural annihilation."

"The objective – I quote from Sir John A. Macdonald, our revered forefather – was to 'take the Indian out of the child,' and thus solve what was referred to as the Indian problem. 'Indianness' was not to be tolerated; rather it must be eliminated. In the buzz-word of the day, assimilation; in the language of the 21st century, cultural genocide." She made clear that this treatment extended well into the 20th century.

John Borrows, Canada Research Chair in Indigenous Law at the University of Victoria, called the Chief Justice's use of the term "unparalleled" in Canadian history.

He said the term is unlikely to have legal consequences, but carries symbolic importance coming from the Chief Justice. "A lot of indigenous people and other people have been asking for that word to be part of our vocabulary because it does more fully communicate the weight of what happened."

Peter Russell, a political science professor emeritus at the University of Toronto, said that Chief Justice McLachlin shares with virtually all Supreme Court judges since a landmark rights case in 1990 "a tremendous sense of sorrow about the denial of very fundamental rights to Canada's native people."

Chief Justice McLachlin, who has been on the court since 1989 and chief since 2000, is its longest-serving chief justice. She cited early laws barring treaty Indians from leaving reservations, rampant starvation and disease and the denial of the right to vote.

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She also pointed to the outlawing of aboriginal religious and social traditions, such as the potlatch and the sun dance, and to residential schools, in which children who had been taken from their parents "were forbidden to speak their native languages, forced to wear white man's clothing, forced to observe Christian religious practices and sometimes subjected to sexual abuse.

The objective was to 'take the Indian out of the child,' and thus to solve what John A. Macdonald referred to as the 'Indian problem.'"

Chief Justice McLachlin authored the court's unanimous ruling last June that legal observers called the most important aboriginal-rights decision in Canadian history. The court determined that native Canadians still own their ancestral lands, unless they signed away their ownership in treaties with government. While they do not retain absolute control, the ruling gives them enormous leverage in negotiations with outside parties that wish to develop their lands. The court granted title to the Tsilhqot'in Nation to an area more than half the size of greater Vancouver, though only 400 people lived there when when the British Crown asserted its sovereignty in 1846.

In her speech, she said Canada had learned from its mistakes, and she cited Prime Minister Stephen Harper's 2008 apology to aboriginal peoples for the abuses of the residential schools.

The event was held in partnership with The Globe and Mail.