The foreign secretary beat her rival, former finance minister Rishi Sunak, by 81,326 votes to 60,399 after a summer-long internal competition sparked by the resignation of Boris Johnson in July.
Truss will become the 15th British Prime Minister under the reign of the head of state, Queen Elizabeth II.
The monarch will ask Liz Truss to form a government on Tuesday, once Boris Johnson officially tenders his resignation.
Here is a list of the former occupants of 10 Downing Street since the Queen’s accession to the throne in 1952:
QUEEN ELIZABETH II’S 15 PRIME MINISTERS
Winston Churchill (Conservative, 1951-55)
Anthony Eden (Conservative, 1955-57)
Harold Macmillan (Conservative, 1957-63)
Alec Douglas-Home (Conservative, 1963-64)
Harold Wilson (Labour, 1964-70)
Edward Heath (Conservative, 1970-74)
Harold Wilson (Labour, 1974-76)
James Callaghan (Labour, 1976-79)
Margaret Thatcher (Conservative, 1979-90)
John Major (Conservative, 1990-97)
Tony Blair (Labour, 1997-2007)
Gordon Brown (Labour, 2007-10)
David Cameron (Conservative, 2010-16)
Theresa May (Conservative, 2016-19)
Boris Johnson (Conservative, 2019-22)
- Editor/ main report by AFP