Cote, 56, is the first woman ever appointed directly to the country's top court from the bar, but follows in the footsteps of a number of distinguished former jurists, including John Sopinka and Ian Binnie.
Her appointment will bring the complement of women on the top court to four of nine justices. It also ends more than a year of unprecedented, roiling controversy over the Supreme Court's composition, which began when Harper's proposed choice of Justice Marc Nadon for a vacant Quebec seat was challenged and ultimately rejected on constitutional grounds by the Supreme Court itself last March.
Cote replaces Justice Louis LeBel — who reaches the court's mandatory retirement age of 75 this weekend — as the third of three mandatory Quebec justices on the bench.
Harper has now locked up Quebec's representation on the country's top court until past the year 2030, and has appointed seven of nine judges in all.
"With her wealth of legal knowledge and decades of experience, Ms. Cote will be a tremendous benefit to this important Canadian institution," the prime minister said in a statement.
"Her appointment is the result of broad consultations with prominent members of the Quebec legal community and we believe she will be a valued addition to Canada's highest court."
Cote's appointment, like Harper's choice of Justice Clement Gascon last June, met with widespread approval — even from opposition critics who decry the Conservative government's decision to scrap a formal parliamentary vetting process in the wake of the Nadon fiasco.
"She's a brilliant lawyer — no problem with that," said Francoise Boivin, the NDP justice critic.
"On the process, though, I still have a lot of questions."
Michele Hollins, president of the Canadian Bar Association, issued a release saying "the justice system and all Canadians will be well-served by the high calibre of today's appointment to the Supreme Court."
Beverley McLachlin, Canada's chief justice, rolled out the welcome mat.
"She brings extensive expertise in commercial and civil law, as well as a wealth of experience in public law," McLachlin's statement said. "I look forward to her contributions to the court."
Cote, a member of the Quebec bar since 1981, is the head of the Montreal litigation group at law firm Osler, Hoskin & Harcourt LLP.
She represented the Quebec Liberal government at the Bastarache Commission, an inquiry into allegations of improper judicial appointments, where Cote established a reputation as a dogged, aggressive intervener.
She also represented Jean Pelletier, Jean Chretien's former chief of staff, when he was fired as president of Via Rail, and she was part of the process of reviewing the judicial conduct of outspoken Quebec Justice Andree Ruffo, who was forced to resign.
Cote has lectured at the Universite du Quebec a Rimouski and the Universite de Montreal.
Carissima Mathen, a constitutional law professor at the University of Ottawa who specializes in the Supreme Court, said Cote's legal background is consistent with others who were appointed from private practice.
Previous direct appointments from Quebec have included Justice Yves Pratte, Justice Louis-Philippe de Grandpre, Justice Louis-Philippe Pigeon and Justice Robert Taschereau, according to the Justice department, and there have been many others from English Canada through the court's 139-year history.
Cote is a senior litigator from a prominent firm, nationally recognized in her field with high-profile public work on her record as well as teaching experience.
"I think she's an entirely solid and credible appointment," said Mathen.
Direct appointments to the top court from the bar seem to occur only about once a generation, said Mathen, "and I'm glad to see that tradition continued."
"I think it brings a valuable perspective that can really round out the court as a whole."
Cote joins a Supreme Court that is poised to deal with a series of thorny legal appeals, including assisted suicide, polygamy, mandatory minimum gun crime sentences and what to do with Quebec's contested gun registry data.
A paper released Thursday by the Macdonald-Laurier Institute, an Ottawa think-tank, found that the Supreme Court has been "remarkably united" under McLachlin in handing the Harper government a recent series of significant legal losses.
Author Benjamin Perrin, who served as legal counsel to Harper's PMO, examined 10 judgments and found the government on the losing end of all but one.
He declared the court 2014's "Policy-Maker of the Year" — a backhanded compliment that fits into long-held Conservative complaints about "activist courts" and "judge-made law."
"The court, no doubt, would resist such a label on the view that it simply applies the law," Perrin writes.
It is into this politically loaded environment that Cote will be thrust as a rookie jurist.
Liberal MP Irwin Cotler, a former justice minister, said he respects Cote's career credentials and doesn't want to contest her appointment.
"You don't want to undermine her as an appointee or the court by engaging in that kind of public critique," said Cotler.
He said the real issue is a more transparent process for judicial appointments, "which at the end of the day would provide a much better expression of respect for the court, for its independence, for Parliament, for the public and for us going forward."
The Conservatives said they consulted the Quebec government; Canada's chief justice, Quebec's chief justice as well as the chief justice of the province's superior court; the Canadian Bar Association; and the Barreau du Quebec.
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