With the defeat of the Conservatives in the 2015 federal election, he was considered a potential candidate to succeed Stephen Harper as permanent leader of the party.

[4] Since the race, he moved back to Nova Scotia and is now a senior counsel with the law firm McInnes Cooper, and a strategic advisor with Deloitte Canada.

MacKay has publicly stated that the major impetus for his entry into federal politics was his frustrations with the shortcomings in the justice system, particularly his perception that the courts do not care about the impact crime has on victims.

[11] MacKay was re-elected in the 2000 federal election and was frequently touted by the media as a possible successor to PC Party leader Joe Clark.

Many of his initial supporters referred to his strong performances in the House of Commons and magnetism as key attributes that would make him a popular leader.

MacKay was appointed House Leader of the new PC-DR Parliamentary Coalition Caucus when it was formally recognized as a political body on September 10, 2001.

Ultimately, his candidacy was helped by the absence of so-called "dream candidates" such as provincial Progressive Conservative Premiers Bernard Lord, Mike Harris and Ralph Klein who did not run for the leadership.

From the onset of the campaign, MacKay insisted that his primary goal upon assuming the leadership would be the rebuilding the fractured conservative movement from within the PC tent.

Some analysts noted that the eliminated third-place challenger David Orchard drew his 25% bulk of delegate supporters largely from the Western prairie provinces.

[citation needed] The agreement also included re-examining the PC Party's policies on government subsidies for national railways and preserving the environment.

The agreement prompted much outrage and controversy amongst United Alternative supporters and was ribaldly referred to by CA MP Jason Kenney as "a deal with the Devil".

MacKay's conservative rival Stephen Harper suggested that the PC Party had hit rock-bottom when its policies and directions would be beholden to a "prairie socialist.

[citation needed] Public musings that the divided PCs would be marginalized in a future election between a relatively stable western-based CA under Stephen Harper and the massively popular Paul Martin Liberals (although Jean Chrétien remained the Liberal leader until November 2003, he had announced he would not run again), MacKay encouraged talks between high-profile members of the Canadian Alliance and the Progressive Conservatives.

[citation needed] Some PC caucus members refused to accept the merger: long-time MP and former Prime Minister Joe Clark continued to sit as a "Progressive Conservative" for the remainder of the Parliament, as did MPs John Herron and André Bachand, while Scott Brison left the new party to join the Liberal Party in December 2003.

There was speculation that MacKay would return to the province to pursue provincial politics and enter the Progressive Conservative Association of Nova Scotia leadership race to become the Premier.

During this period MacKay and the Conservative Party of Canada joined the Bush Administration in opposing the United Nations' call for a ceasefire.

"[23] The incident happened on the same day that a suicide bomber detonated an explosive in Baghlan in the northeastern part of the country killing at least 75 including several politicians.

[24] In 2008, MacKay announced a broad exhaustive and very expensive program to upgrade the Canadian military's equipment, spending over $400 billion over 25 years.

In July 2010, MacKay was accused of inappropriately using public funds when he combined the use of a Canadian Cormorant military helicopter for both a search and rescue demonstration, and to transport the minister from a private fishing camp in Newfoundland to Gander Airport.

[25] MacKay, then the Minister of National Defence, defended his use of the military helicopter stating, "Three days into the visit I participated in a search and rescue demonstration with 103 squadron 9 Wing Gander.

[26] On June 5, 2012, it was revealed that a widely publicized 2010 news conference announcing Conservative plans to buy 65 F-35 Stealth Fighters had cost $47,000.

Documents provided to parliament by Peter Mackay indicated that Lockheed Martin had delivered the F-35 mockup used in the photo-op for free, and that the cost was primarily for services to support the news conference and one hundred invited guests.

[27] On July 15, 2013, the cabinet was shuffled, and Mackay became the Minister of Justice and Attorney General of Canada, replacing Rob Nicholson, who took over the defence portfolio.

[28] On March 5, 2014, MacKay generated controversy when, in response to opposition Liberal MP Kevin Lamoureux, he tossed documents purporting to concern the issue of missing and murdered Aboriginal women onto the floor of the House of Commons.

[39] On October 10, 2019, The Globe and Mail reported that MacKay supporters were preparing to launch a leadership bid should Conservative Party leader Andrew Scheer fail to secure a government in the 2019 federal election.

MacKay responded to questions by saying that he was "not [aware]" of Conservatives backers organizing a campaign, and that he was "doing everything I can to help Andrew and support him and his team.

[4] After the vote, it was revealed that MacKay spent $124,000 on security during the campaign[44] in response to numerous death threats that were lodged against him and his family.

"[48] MacKay had been seen in public dating Jana Juginovic, director of programming at CTV News Channel, after having kept their relationship private for many months.

She is co-founder and president of Stop Child Executions, a human rights group whose aim is to focus world attention on the plight of young people on death row in Iran.

A sports enthusiast, MacKay was active in local rugby, baseball, football and hockey teams in Pictou County, Nova Scotia.