David Johnston, Canada's governor general-designate, is shown meeting the Queen alongside Prime Minister Stephen Harper during a dinner held in her honour in Toronto on Monday. (Prime Minister's Office)

David Johnston, announced as Canada's next governor general on Thursday, is pledging to be a "stalwart defender" of Canada's heritage, institutions and people.

After weeks of speculation, the Prime Minister's Office said the Canadian legal scholar and president of the University of Waterloo has been approved by the Queen and will take over on Oct. 1 after Gov. Gen. Michaëlle Jean's term ends.

In a statement to reporters from the Senate foyer in Ottawa, Johnston called the appointment a "mark of confidence that touches me profoundly." He also noted his predecessors, from Samuel de Champlain to Jean, have set a "fine example" for him to follow.

"I've had the good fortune to witness Canadians' creativity and our ties to the world, as well as our diversity and our vitality," he said. "The opportunity to see these values at work across the country means a great deal to me."

In a statement, Prime Minister Stephen Harper hailed Johnston's selection, saying the 69-year-old Ontario scholar "represents the best of Canada."

"He represents hard work, dedication, public service and humility," Harper said. "I am confident he will continue to embody these traits in his new role as the Crown's representative in Canada."

Johnston also said he looked forward to meeting with members of the Canadian Forces.

Ignatieff: Johnston 'ideal choice'

In a statement following the announcement, Liberal Leader Michael Ignatieff congratulated Johnston and said his legal expertise and dedication to learning and innovation made him an "ideal choice."

Ignatieff also praised Jean for "passionately carrying out her duties with grace and dignity."

He paid tribute to her dedication to the military and aboriginal Canadians, as well as particularly her native country, Haiti, following this year's earthquake.

"Her heartfelt warmth and kindness touched so many in Canada and abroad," he said.

Jean, Governor General since Sept. 27, 2005, will serve as UNESCO's special envoy in Haiti after her term ends.

While others praised Johnston's appointment, the grand chief of the Assembly of Manitoba Chiefs said he was disappointed.

Given the progress made between the federal government and aboriginal people with the apology for residential schools and the Truth and Reconciliation Commission, Chief Ron Evans said appointing an aboriginal person to Rideau Hall seemed the next logical step.

But he said the progress "has a long ways to go to demonstrate to what length that it wants to make things right with indigenous people, and I believe that this was an opportunity for them to do that because we have a lot of talent out there," Evans told CBC News.

He added there may be discussion at next week's annual general assembly about writing a formal letter to the federal government requesting an aboriginal person be considered for governor general next time.

But Evans vowed to work with whomever fills the position.

Advised PM on Schreiber inquiry terms

Johnston, born in Sudbury, Ont., is perhaps best known for advising the federal Conservative government on what shape a public inquiry into the dealings between former prime minister Brian Mulroney and businessman Karlheinz Schreiber should take.

Johnston has served on numerous provincial and federal task forces and committees. He is widely considered as an expert in constitutional law, which observers have said could serve him well in an age of fragile minority governments and potential constitutional crises.

"Look at his background and his academic background in particular, and I sense that he will be able to stand up to anyone," NDP MP Paul Dewar told CBC News on Thursday.

Jean, appointed in 2005, generated considerable national attention and triggered a fierce debate over the governor general's role when she twice granted Harper's requests to prorogue Parliament.

The first time came in December 2008 when Harper's Conservative government was under threat of defeat in the House of Commons at the hands of a proposed coalition between the Liberals and NDP with the signed support of the Bloc Québécois.

The governor general is appointed by the Queen on the advice of the prime minister and acts as the Queen's representative in Canada and Canada's de facto head of state. The term is five years and can be extended to seven.

Johnston taught law at Queen's University in Kingston, Ont., and the University of Toronto after earning degrees at Queen's, Harvard University and Cambridge University.

He was also the principal and vice-chancellor of McGill University in Montreal, and dean of the faculty of law at the University of Western Ontario in London.

An author of several books, Johnston is also a companion of the Order of Canada.

Johnston shook hands with Queen Elizabeth on Monday in Toronto, but it was not a formal meeting. He is expected to travel to England to officially meet with the Queen this summer.

He and his wife, Sharon Johnston, have five daughters.

With files from The Canadian Press