Mary Elizabeth Truss is a British politician who served as Prime Minister of the United Kingdom and Leader of the Conservative Party from September to October 2022. On her fiftieth day in office, she stepped down amid a government crisis, making her the shortest-serving prime minister in British history. The member of Parliament (MP) for South West Norfolk since 2010, Truss previously held various Cabinet positions under three prime ministers—David Cameron, Theresa May and Boris Johnson—lastly as foreign secretary from 2021 to 2022.

The prime minister of the United Kingdom is the head of government of the United Kingdom. The prime minister advises the sovereign on the exercise of much of the royal prerogative, chairs the Cabinet and selects its ministers. As modern prime ministers hold office by virtue of their ability to command the confidence of the House of Commons, they sit as members of Parliament. The current prime minister is Rishi Sunak of the Conservative Party, who assumed the office on 25 October 2022.