She made the news at No.10 Downing Street in London, saying she had informed King Charles that she was retiring as Conservative Party leader.
She continued: “I recognise… given the situation I cannot deliver the mandate on which I was elected by the Conservative Party.”
Liz Truss has been Prime Minister for only 45 days, the shortest term of any British Prime Minister.
Her departure came amid a British economic crisis and a series of policy reversals by her administration that severely weakened Truss’s authority.
Her declaration came on Thursday, her 45th day in office.
Speaking outside Downing Street, Truss stated that she was unable to deliver on the mandate for which she was elected and that she would quit the position once her replacement was chosen in a party leadership election.
George Canning, who died in 1827, had the second-shortest tenure as Prime Minister, serving for 119 days.
