Since Confederation, Canada has had 23 Prime Ministers varying in age from 39 to 70. Below is a list of the 5 youngest Prime Ministers to ever lead Canada.
#5 Kim Campbell
After the 1993 resignation of then Prime Minister Brian Mulroney, a leadership race took place within the Progressive Conservative party. Kim Campbell won the race and was officially appointed Prime Minister on June 25th at the age of 46 years and 107 days. Unfortunately for Campbell, she would make several missteps and unpopular statements leading up to the October election which resulted in a devastating loss. Campbell was Prime Minister for just 132 days before losing the election and resigning as party leader.
#4 Arthur Meighen
Quite possibly the most forgotten Prime Minister in Canadian history was also the 4th youngest. More surprisingly is that Arthur Meighen was Prime Minister not once but twice and was never actually elected either time. Due to a series of circumstances, including the highly controversial King–Byng Affair, Meighen was appointed Prime Minister twice without an election. His first appointment was made in 1920 at the age of 46 years and 24 days making him the 4th youngest Prime Minister for six months. Including his second appointment in 1926, Meighen was only Prime Minister for a total of 625 days.
#3 Brian Mulroney
One of Canada's most recognizable Prime Ministers was also the second youngest person to lead the country at the time. Mulroney led the Progressive Conservative party to a majority victory and became Prime Minister on September 17th 1984 at the age of 45 years and 181 days. Unlike the two previously mentioned young leaders who each stayed in power for just a few hundred days, Mulroney held his position for nearly 9 years. He maintained a majority government through two terms as PM but became increasingly unpopular after numerous scandals emerged and the introduction of the GST. As a result, Mulroney made the decision to resign before the 1993 election.
#2 Justin Trudeau
Despite what many may think, Justin Trudeau is not the youngest person to become Prime Minister of Canada. After winning a majority victory in the 2015 election, Trudeau became Canada's second youngest Prime Minister at the age of 43 years and 314 days. Trudeau has maintained an approval rating of over 60% since being elected and has made headlines around the globe for his good looks and charm. Ironically, Trudeau is the only non-conservative leader out of the top 5 youngest PM's despite being criticised by the Conservative party for being too young and inexperienced.
#1 Joe Clark
At the age of 36, Joe Clark became the youngest person to lead a major Canadian political party after winning the Progressive Conservative leadership race in 1976. Just three years later, Clark led the party to victory in the 1979 election and took office just one day before his 40th birthday. To this day, Clark remains the only person in Canadian history to become Prime Minister while still in their 30s (even if it was for just a few hours). Clark remained PM for close to four years before losing the 1980 election after facing harsh criticism for introducing a gas tax despite promising to reduce taxes.