Beverley McLachlin, the longest-serving Chief Justice in the history of the Supreme Court of Canada — and the first woman ever to hold the post — will retire from the top court on December 15 this year.

“It has been a great privilege to serve as a justice of the Court, and later its Chief Justice, for so many years,” McLachlin wrote in a statement sent to reporters Monday afternoon. “I have had the good fortune of working with several generations of Canada’s finest judges and best lawyers. I have enjoyed the work and the people I have worked with enormously.”

Before she was appointed to the Supreme Court by former prime minister Brian Mulroney in the spring of 1989, McLachlin, now 73, practised law in both British Columbia and Alberta. She served on the Supreme Court of British Columbia from 1981 to 1985 and subsequently the B.C. Court of Appeal from 1985 to 1988.

She has served on the Supreme Court of Canada for 28 years — 17 of those as Chief Justice. McLachlin replaced former Chief Justice Antonio Lamer.

During her tenure, she has presided over a number of groundbreaking decisions by the top court on the topics of First Nations rights, Canada’s prostitution laws, prisoners’ rights to vote and, more recently, Canadians’ right to medically-assisted death.

Several constitutional law experts and university professors said they expect McLachlin’s judicial legacy will be a consequence of her leadership of the court through those landmark rulings.

“Even though it hasn’t always be the case, I think she’ll be remembered for how often she brought the court together in difficult and important decisions where they needed to speak as one,” said Lorne Sossin, dean and professor of law at York University. “I think those moments of such nine different people with so many different views coming together always reflects the leadership of a Chief Justice who can be a principled pragmatist … who can stand for things but willing to compromise to bring people together.

“That, I think, is a real legacy.”

Emmett Macfarlane, a professor of political science at the University Waterloo who has written a book on the Supreme Court of Canada, said McLachlin also “modernized” the top court by “opening it up to the public and media in ways her predecessors wouldn’t.”

However, Macfarlane questioned whether it’s “healthy” to have one person at the helm of such a powerful, democratic institution for nearly 20 years, despite their skill or success.

“I think there’s something to be said for having a greater diversity of voices help shape the law and the nation’s highest court,” Macfarlane wrote in an email.

Talk of diversity on the Supreme Court bench ramped up Monday as experts weighed in on prospects for McLachlin’s replacement.

By convention, the regional makeup of the Supreme Court is three justices from Quebec, three from Ontario, two from Western Canada and one from Atlantic Canada. Given McLachlin came to the top court from B.C., Macfarlane and University of Ottawa law professor Errol Mendes both said her retirement will present a “prime” opportunity for the prime minister to appoint Canada’s first indigenous Supreme Court justice.

“I think its overdue,” Mendes said, adding that he once advocated for the appointment of an aboriginal judge when an Ontario seat on the Supreme Court became vacant. “Given (the importance of) the First Nations issues that are coming up … absolutely there’s a very good possibility that we could find an excellent candidate from B.C. if we stick to the tradition of appointing a judge from where the retiring judge is coming from.”

Some academics and advocates who hoped that the Liberal government’s new selection process for Supreme Court justices would attach less importance to the convention of regional seats expressed disappointed last year when Prime Minister Justin Trudeau named Malcolm Rowe of Newfoundland to the top court instead of a visible minority judge.

There was speculation as well on Monday about who might replace McLachlin as Chief Justice. A few experts predicted the prime minister would select one of the justices representing Quebec, the most senior of whom is Justice Richard Wagner.

In 2014, McLachlin found herself at the centre of a political and media firestorm when then-prime minister Stephen Harper’s office suggested she had inappropriately tried to intervene in the government’s process to appoint Federal Court Judge Marc Nadon to the Supreme Court.

McLachlin issued a rare public statement in response to the allegations, which said the Chief Justice had advised then-justice minister Peter MacKay that there might a “potential problem” in naming Nadon to represent Quebec on the top court’s bench, but she had not lobbied against the appointment.

“I think she showed her courage when she basically saw that there was a danger to the nature of the court and … when she felt that she had to disagree with the prime minister in terms of the appointment,” Mendes said of the public disagreement.

The Supreme Court of Canada rejected Nadon’s appointment in March 2014, ruling that he was not eligible to fill the then-vacant Quebec seat because he had served as a Federal Court judge in Ottawa for the past two decades – and was also not a current member of the Quebec bar.

The ruling marked the first time in its history that the court had been asked to rule on the qualifications of a potential colleague.

In reaction to the news that McLachlin will retire from the Supreme Court at the end of the year, federal politicians across parties called the Chief Justice a “trailblazer.”

“Chief Justice McLachlin’s judicial accomplishments are unparalleled in Canadian history,” Trudeau said in the written statement to reporters. “After 28 years at the Supreme Court of Canada, her contributions reach into every part of our law. Canadians owe her an immense debt.”

Alistair MacGregor, the New Democrats’ justice critic, said McLachlin will be “impossible to replace,” while his Conservative counterpart Michael Cooper said she has “left an enduring mark on the Supreme Court of Canada.”

“The decisions she’s written are redefining what it is to be Canadian and in a very real way,” Green Party Leader Elizabeth May said.”

The federal justice minister also reacted to the news of McLachlin’s impending departure on Twitter Monday.

“Gilakas’la Madame Chief Justice McLachlin. For so many reasons, you have solidified your place in our country’s legal history,” Jody-Wilson Raybould tweeted.

McLachlin’s announcement Monday did not come as a great surprise to the legal community. Under federal law, Supreme Court justices must retire at the age of 75.

Sources told the Financial Post two weeks ago that McLachlin has penned a novel, which she plans to publish after she retires.