Shortest-serving UK Prime Ministers Despite talk of running for a third term, Boris Johnson has been forced to resign as British Prime Minister SHORTEST-TERM PRIME MINISTERS SINCE 20TH CENTURY Conservative Labour James Callaghan 1976-79 3 years 29 days Theresa May 2016-19 3 years 11 days Boris Johnson 2019-22 2 years 348 days Neville Chamberlain 1937-40 2 years 348 days Gordon Brown 2007-10 2 years 318 days 1 year 279 days Sir Anthony Eden 1955-57 363 days Sir Alec Douglas-Home 1963-64 211 days Andrew Bonar Law 1922-23 119 days Shortest ever term: George Canning 1827 Years 1 2 3 Although Johnson will stay in Downing Street until the autumn, term defined as period between appointment and resignation, therefore term has ended Source: UK Government Picture: Getty Images © GRAPHIC NEWS