Johnston was the special rapporteur appointed to investigate reports of foreign interference in recent Canadian federal elections until his resignation on June 9, 2023.

He was in 2010 appointed as governor general by then monarch Queen Elizabeth II, on the recommendation of then Prime Minister of Canada Stephen Harper, to replace Michaëlle Jean as viceroy[3] and he occupied the post until succeeded by Julie Payette in 2017.

[7] Johnston graduated from high school and moved on to Harvard University in 1959,[9][10] earning his Bachelor of Arts degree, magna cum laude, in 1963.

During that period, the couple acquired a home in Heidelberg, Ontario,[21] and began operating an adjacent horse training ranch, Chatterbox Farm.

He also moderated the provincial leaders' debate featuring David Peterson, Bob Rae, and Larry Grossman, in the run up to the Ontario general election in 1987.

[33] Johnston has also acted as moderator of two public affairs panel discussion programmes, The Editors and The World in Review, which aired in the 1990s on both CBC Newsworld in Canada and PBS in the United States.

[32] Investigations commissioned by both federal and provincial Crowns-in-Council have been chaired by Johnston, starting with the National Round Table on the Environment and the Economy in the late 1980s,[34] followed by the National Task Force on High Speed Broadband Access, the Committee on Information Systems for the Environment, the Advisory Committee on Online Learning, Ontario's Infertility and Adoption Review Panel between 2008 and 2009, and other scientific or public policy panels.

[21] On November 14, 2007, Johnston was appointed by Governor General Michaëlle Jean, on the advice of Prime Minister Stephen Harper, as an independent adviser and charged with drafting for the Cabinet the terms of reference for the public inquiry, known as the Oliphant Commission, into the Airbus affair.

[34] This appointment itself, however, was criticized by the independent citizens' group Democracy Watch as a conflict of interest, given that Johnston had once reported directly to Mulroney during the latter's time as prime minister.

[38] He did not, however, include as a subject the awarding of the Airbus contract, on the basis that this aspect had already been investigated by the Royal Canadian Mounted Police, prompting criticism from opposition members of parliament and accusations that Johnston had acted as the Prime Minister's man.

[39] This intensified after it was later revealed that Mulroney had accepted $300,000 in cash from Karlheinz Schreiber, but Oliphant could not examine any possible link between that payment and Airbus due to the narrow scope of the commission's mandate.

[40] Others, though, such as Peter George, then-president of McMaster University,[41] and subsequently the editorial board of The Globe and Mail,[42] as well as Andrew Coyne in Maclean's,[43] defended Johnston, detailing his integrity and independence.

[49][50] A special search committee convened by the Prime Minister recommended Johnston for the viceregal position; the group was headed by Sheila-Marie Cook, secretary to the Governor General,[51] and further consisted of Kevin MacLeod,[11] the Canadian Secretary to the Queen, Usher of the Black Rod of the Senate of Canada, and parliament's top protocol officer; Christopher Manfredi, dean of the Faculty of Arts at McGill University; Rainer Knopff, a political scientist at the University of Calgary; Father Jacques Monet, of the Canadian Institute of Jesuit Studies; and Christopher McCreery, historian and private secretary to the Lieutenant Governor of Nova Scotia.

[53] The appointment was widely praised, its announcement garnering positive words from individuals like former University of Toronto president Robert Prichard, columnist Andrew Coyne,[43][54] and Opposition Leader Michael Ignatieff.

The president of Quebec's Conseil de la souveraineté, Gérald Larose, declared Johnston to be an "adversary" of Quebec independence and Mario Beaulieu, head of the Saint-Jean-Baptiste Society, called the nomination of Johnston "partisan" and the governor general-designate himself a "federalist extremist",[47] statements that columnist Richard Martineau criticized for creating a "fake scandal", since any Governor General of Canada would advocate for Canadian unity.

On the return coach ride from Parliament Hill to Rideau Hall, the viceregal couple stopped to lay the bouquet at the Tomb of the Unknown Soldier.

[64] On November 4, the Governor General made his first visit to Afghanistan to meet with Canadian troops serving there and the Afghan forces they were training;[65] similar visits to Afghanistan followed through Johnston's tenure, including a Christmas spent with Canadian Forces personnel stationed at Camp Alamo and Camp Black Horse,[66] as did meetings with members of the military in other locations overseas.

[67] Johnston undertook his first state visits in February and March 2011, journeying to Kuwait (to attend its 50th Independence Day and take part in the celebrations of the fifth anniversary of the accession of Emir Sabah Al-Ahmad Al-Jaber Al-Sabah) and Qatar.

The speech Johnston delivered on August 14, 2011, to the Canadian Bar Association's annual meeting in Halifax, Nova Scotia, attracted media attention[70] for its criticism of the legal profession: the Governor General lamented unnecessary and deliberate legal delays across Canada, the role of unscrupulous American lawyers in the unfolding of the 2007–2008 financial crisis, and said the profession was losing the public's trust.

[70][71] These comments were noted for being unusually controversial for a viceroy, but Johnston's colleagues and the editorial board of The Globe and Mail found the Governor General's words to be both unsurprising and welcome.

[71][72] In keeping with his focus on education, the Governor General, beginning in his early months in office and continuing throughout his time there, visited a number of universities across Canada, attending conferences, delivering lectures, and speaking at convocations.

[98] He called for expanded education about the residential school system and said "this is a moment for national reflection and introspection... to think about the depth of our commitment to tolerance, respect and inclusiveness, and whether we can do better.

"[104] As part of his efforts to promote education and research, Johnston, beginning in 2012, annually hosted the Killiam Award Symposium at Rideau Hall.

[7] In late 2016, the Governor General hosted a conference on concussions, declaring head injuries in sports to be a "public health issue",[7] and criticized the NHL's position on fighting in hockey.

On November 1, 2013, he hosted Prince Edward, Earl of Wessex, at the 50th anniversary of the Duke of Edinburgh's Award royal gala, held at Rideau Hall.

The first, in October 2013, came shortly after Xi had become president, and overlapped with visits by cabinet ministers, and was aimed at smoothing relations and promoting the government's economic agenda.

[114][115] During the trip, Johnston also met with several Chinese officials, including Premier Li Keqiang, to discuss ways to deepen educational and cultural ties between Canada and China.

The Governor General delivered over 1,400 speeches and awarded tens of thousands of honours, medals, and special commemorations and welcomed 1.5 million Canadians to Rideau Hall and the Citadel.

[131][132] However, he resigned the post after Trudeau,[133] on March 15, 2023, chose Johnston to act as special rapporteur investigating Chinese government interference in the 2019 and 2021 Canadian federal elections.

[134][135] Politicians and journalists voiced both disapproval—concerns mainly focusing on Johnston's relationship with the Trudeau family, membership in the Pierre Elliott Trudeau Foundation, and state visits to China he made as governor general[143]—and approval—citing his experience as a legal scholar and dean of law and the trust placed on him by Harper to act as an impartial referee while serving as governor general during a period of parliamentary instability.