Truss beats George Canning, who was prime minister for 119 days in 1827.
With yet another prime minister's resignation, the British government's 10 Downing Street looks like a revolving door. Analysts blame polarization, populism, a flawed system and poor leadership.
After a bruising first six weeks in office, the prime minister replaced her finance chief with former leadership rival Jeremy Hunt. But she still faces a barrage of criticism.
In a move to calm financial markets and her own Conservative Party, Prime Minister Liz Truss canceled planned tax cuts for corporations and replaced Kwasi Kwarteng as treasury head with Jeremy Hunt.
Britain's prime minister steps down after several top officials quit his government, saying they couldn't serve under his scandal-tarred leadership.
If Johnson does not heed calls to resign — and he insists he won't — he could be toppled through a no-confidence vote.