Has a party that won an election ever lost its leader in the process?

Question

In a Parliamentary democracy, general elections appoint constituency representatives. Most such appointees are members of parties with internally determined leaders. One or more parties then form a government, with one of these party leaders the head of government. However, it's theoretically possible that a party that enters or stays in government due to its electoral performance has to change leader, due to that individual losing their seat. (Party leaders typically come from safe seats to prevent this.) Has this ever actually happened? I'd be interested if this happened in the UK, or failing that in any nation with a Westminster system.

Answer 1

This actually just happened in Canada while I was there! Two parties, the Conservatives (right-leaning) and the New Democratic Party (left-leaning, liberal allies), had leaders who lost their elections in the upset Liberal victory in Canada's 2025 election. Jagmeet Singh placed third in his British Columbia riding and resigned following the election. His party won so few seats that they lost status in the House of Commons. In Ontario, Pierre Pollievre 's party was leading in the polls heavily, but due to US election results and the resignation of Justin Trudeau the liberals slimly won and Pierre failed to win his seat in Ontario. Pierre then had to run in a special Alberta election to regain a seat to continue leading his party.