She is the shortest-serving PM in recent UK history.
Liz Truss has resigned as UK prime minister after just 45 days in office.
Speaking outside of 10 Downing Street on Thursday afternoon, she announced there will be another leadership election within the ruling Conservative Party, which will decide who succeeds her.
This makes Truss the shortest-serving PM in UK history, paving the way for the country's fourth leader in little over three years. Her replacement will be appointed in the coming week.
Announcing her resignation, Truss said she arrived in office during a "time of great economic and international instability."
“We delivered on energy bills and cutting national insurance," she continued. "We set out a vision for a low tax high growth economy that would take advantage of the freedoms of Brexit."
But added: “Given the situation, I cannot deliver the mandate on which I was elected."
Truss lost the faith of her party after her tax-cutting policies, which were largely seen as economically irresponsible and as benefiting the wealthy, triggered market turmoil and caused public support to collapse in the polls.
She will remain in office until a successor has been chosen, with a leadership election expected by 28 October.
Opposition parties have called for a national election.
Her former leadership rival Rishi Sunak is the favourite to take over, followed by Leader of the House of Commons Penny Mordaunt and Defence Secretary Ben Wallace. Former PM Boris Johnson is in fourth.
In her resignation speech, Truss said a leadership election will "will ensure we remain on a path to deliver our fiscal plans and maintain our country's economic stability and national security."
Truss is the shortest-serving PM in British history, replacing the last record holder George Canning who died of ill health in 1827 after 119 days in office.
Her resignation means the UK will have its fourth prime minister in just over three years. Its previous four PMs -- David Cameron, Gordon Brown, Tony Blair and John Major -- were in office for a combined 26 years.
A comic campaign by the British newspaper the Daily Star had set up a live stream asking whether a lettuce would outlast the UK PM, which they likened to the vegetable.
It appears the lettuce has won.
Truss only became prime minister on 6 September after beating former finance minister Rishi Sunak in a Tory leadership contest.
But her short period in charge was disastrous.
A botched economic plan unveiled by the government last month triggered financial turmoil and a political crisis that has seen the replacement of Truss’ finance minister, multiple policy U-turns and a breakdown of discipline in the governing Conservative Party.
On Wednesday, a senior minister quit her government with a barrage of criticism and a vote in the House of Commons descended into chaos and acrimony. This was the spark of Truss's resignation.
Before resigning, Truss had held a hastily arranged meeting in her 10 Downing Street office with Graham Brady, a senior Conservative lawmaker who oversees leadership challenges.
Brady was tasked with assessing whether the prime minister still has the support of Tory members of Parliament — and it seemed she did not.
The value of the pound rallied in response to the PM's resignation, after falling to its lowest-ever level against the dollar following Truss's mini-budget.