In the fall of 1980, Roger Tassé flew to London on a business trip. Canada’s top justice bureaucrat was in the British capital to brief parliamentarians on Prime Minister Pierre Trudeau’s plan to patriate the Constitution, transferring it from Westminster to Canada.

On landing back in Montreal, Mr. Tassé was questioned by a customs agent who wondered why his London trip had only lasted 30 hours.

“I went to pick up our Constitution. I have it in my suitcase!” Mr. Tassé joked.

The customs officer was not amused and selected Mr. Tassé for additional screening.

The wary officer could be forgiven for his ignorance. The slight, quiet man before him wasn’t famous. But he was important.

Mr. Tassé, who died on May 20 at the age of 85, was a key figure in bringing the Constitution home and directing the drafting of the Charter of Rights and Freedoms that is at the heart of the law of the land.

He did this from back rooms, in the margins of memos and in endless meetings. But if his methods were low-key, his impact on the country was no less dramatic for it.

Eddie Goldenberg, a long-time aide to Jean Chrétien, acknowledged Mr. Tassé’s central role in creating a document that has revolutionized Canadian society.

“He was, I would say, the leading figure in pulling it all together,” Mr. Goldenberg said.

Mr. Tassé was born on June 5, 1931, the eldest of the five sons of Léopold Tassé, a bank clerk, and the former Marguerite Martin, a housewife who helped the family finances by sewing gloves.

In his memoirs, published in 2013, Mr. Tassé recalled growing up in working-class Montreal in a house with few books but with parents who expected discipline and hard work from their children. He was studious and earned good grades, which earmarked him for collège classique, the rigorous schools that formed French Canada’s elite at the time.

His attendance at Collège Sainte-Marie would have been beyond his family’s means, but for the fact that the school saw him as potential priesthood material and arranged a $50 annual bursary from a retired prelate.

Following graduation from law school in 1955, with his only other option a law firm in small-town Shawinigan, Que., Mr. Tassé chose the federal civil service in Ottawa.

He started in the Justice Department, handling competition and anti-trust investigations. He also taught evening classes at the University of Ottawa law school in the 1960s, counting among his students a rookie MP named Jean Chrétien.

By the time he became deputy justice minister in 1977, he had a two-decade record as a solid, trustworthy bureaucrat. As superintendent of bankruptcy, he had overseen a complex overhaul of insolvency laws. As deputy solicitor-general, he had to be a steady presence while his ministers were blindsided by revelations that the RCMP had misled them about the scope of the force’s illegal tactics against Quebec separatists. Even before the Charter became law, he had been named an officer of the Order of Canada, in part for the mark he had left on bankruptcy law, the criminal justice system and judicial administration.

Pierre Trudeau’s Liberals were elected in 1980, on the eve of the first referendum on Quebec sovereignty, during which Mr. Trudeau had suggested that a No vote would be a mandate to renew the Constitution. When the federalists won, it meant that Mr. Tassé’s department would have to come up with a plan to draft a Charter of Rights and embed it in a Canadian Constitution patriated from Britain.

Mr. Tassé’s political master was Mr. Chrétien – his former law school pupil. Despite their common rise from humble Quebec backgrounds, the new justice minister and his deputy were a study in contrasts: one a blunt, hyper-partisan street fighter, the other a model bureaucrat, impartial, subtle and soft-spoken.

“They mutually reinforced each other,” said retired Supreme Court justice Ian Binnie, who served under both men.

“Chrétien was the savvy politician who was interested in getting a deal, and Tassé’s job was to make sure it was the right deal.”

During contentious committee hearings on the Charter starting in the fall of 1980, Mr. Tassé was one of two aides flanking Mr. Chrétien as he was grilled by citizen groups, whispering advice to their minister in both official languages, University of Ottawa law professor Adam Dodek reports in a forthcoming book about the making of the Charter. Because Mr. Chrétien’s French was better than his English, Mr. Tassé sat on his right and spoke into his bad ear, while an anglophone bureaucrat spoke into his good ear in English.

After criticism during the hearings that the Charter’s opening section left governments too much leeway for curtailing citizens’ rights, Mr. Tassé masterminded a bit of legal language that said any limits to rights and freedoms outlined in the Charter would have to be “demonstrably justified.”

The new phrasing firmly established the principle that “the onus of infringing a constitutional right has to be placed on the government,” Mr. Dodek said in an interview. “I think this is directly [to] Tassé’s credit.”

Despite the Charter’s lofty ideals, its composition was often ad hoc, as Mr. Tassé and his team of lawyers cobbled together a text that needed to pass muster with a fractious country. As former department lawyer Mary Dawson, who drafted the English text, recalled in the McGill Law Journal, the Charter was written and rewritten on typewriters, with changes made by taping strips of paper onto the page.

Mr. Tassé appreciated the hard work of his staff and he let them know it. During the parliamentary hearings, there were daily meetings in Mr. Tassé’s office before the day’s session and afterward. The day after the committee closed, staff were summoned to the deputy minister’s office one last time.

“I don’t think any of us were very anxious to go,” Mr. Goldenberg said. “And we got to his office and he had a couple of bottles of champagne, just to say thank you for all our work.”

For Mr. Tassé, the time for popping corks lay some distance in the future. With the Charter mostly written, the federal government still had to secure support from the provinces, a vexed role that again fell in part to him.

The deputy minister was among the small group of functionaries who huddled with Mr. Trudeau at 24 Sussex Dr. during the “night of the long knives” in November, 1981, when federal ministers and all the premiers except Quebec’s René Lévesque hatched a deal for repatriating the Constitution.

Rather than rejoice when the package was finalized, Mr. Tassé, a proud Quebecker himself, said in his memoirs that he went home and one of his daughters, a junior college student, harangued him about Quebec not being part of the agreement.

“How could you be happy with this accord?” she asked.

It was a question that would dog Mr. Tassé through the next phase of his career, as a proponent of the doomed Meech Lake and Charlottetown Accords, which attempted to secure Quebec’s consent to the 1982 Constitution Act he had worked so deftly to build.

Though Mr. Tassé retired from the civil service in 1985, the Progressive Conservative prime minister Brian Mulroney contracted him to consult for the government on constitutional affairs as it tried to patch the Quebec-shaped hole in the country’s new constitutional settlement.

Though Mr. Tassé maintained a rigid bureaucratic neutrality on partisan political questions, he had strong convictions about his home province. Along with skiing and tennis, he took a keen interest in Quebec’s distinctive theatre and cinema, Mr. Binnie said, and in his memoirs he describes moving his family to Gatineau so that his children could grow up in French.

“He was a very strong Quebecker,” Mr. Binnie said.

That feeling contributed to a sense that the province deserved special recognition within Canada, which the Meech Lake Accord promised through its contentious “distinct society” clause.

He supported Meech and disagreed with Mr. Trudeau and Mr. Chrétien, who warned that the clause would undermine the Charter.

As Mr. Mulroney recounted, in a rare fit of boastfulness to reassure him about the impact of the Accord, Mr. Tassé reminded him, “You know, Prime Minister, I wrote the Charter.”

Even with his misgivings about Quebec’s exclusion from the “constitutional family,” he continued to defend the Charter against early criticisms. “When it comes to my basic freedoms, in the end I much prefer a safety valve of nine people who are above the tremors of the situation,” he said in an interview with The Globe to mark the fifth anniversary of the Charter’s adoption.

“Above the tremors of the situation” might have been Mr. Tassé’s motto. He had an old-school sense of bureaucratic duty, pledged to compromise and dispassion, former colleagues say. In 1994 he co-authored a book with the characteristically mild title, Canada: Reclaiming the Middle Ground.

The skills that made him an effective mandarin were never flashy.

Dozens of daily memos would be returned overnight, the margins clogged with thoughtful replies in his cramped handwriting.

His endurance of long, tedious meetings was famous. “He could sit there for hours until people talked themselves out,” Mr. Binnie said. “He just sat and listened until they exhausted themselves. It was like Muhammad Ali’s rope-a-dope tactics.”

He could work with politicians, meanwhile, because he understood them – including their limitations. He said of one cabinet member, “If you’re writing a memo for the minister, you can write as much as you want, but he’ll only read the first page.”

“Of all the people I worked with in Ottawa,” Mr. Binnie concluded, “he was the most impressive.”

Mr. Tassé leaves his wife, Renée Marcil; their four children, Anne Marie, Sylvie, Dominique and Louis; and seven grandchildren.

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