Keir Starmer will step down as MP for Holborn and St Pancras after 11 years representing the London constituency.
His resignation from the Commons will trigger a by-election in the Labour stronghold.
Starmer says he will focus on international affairs and continue his work on tackling violence against women and girls.
Sir Keir Starmer has announced he will step down as the MP for Holborn and St Pancras, paving the way for a by-election in the London constituency he has represented for 11 years.
Starmer said he would now turn his attention to international affairs, including defence, security, trade and technology, while continuing his work on tackling violence against women and girls. His decision comes weeks after he stepped down as prime minister, with Andy Burnham succeeding him.
Starmer to leave Parliament
In a statement to the Camden New Journal, Starmer said it had been a "huge honour and privilege" to represent Holborn and St Pancras for 11 years. He said he was now ready to "pass the baton to a successor".
"I will now focus on other things and that will be international affairs including defence, security, trade and technology in a fast-changing world.
"I will also continue, as I have done for a long time now with others, to work on combating violence against women and girls; that is an issue that matters to me hugely.
"It's work I started before I became an MP and it's work I'm keen to continue after I'm an MP. So international affairs on the one hand, and continuing my work on violence against women and girls on the other."
A date for the by-election will not be set until Starmer formally resigns his Commons seat.
Holborn and St Pancras has long been a Labour stronghold. Starmer secured a majority of more than 11,000 votes in the constituency at the 2024 general election.
The announcement came hours before Burnham was due to make his first statement in the Commons as prime minister, when he was expected to outline his priorities and take questions from MPs, BBC reported.
Starmer changes earlier position
Starmer's announcement follows weeks of speculation over whether he would remain an MP after leaving Downing Street.
In a BBC interview shortly after stepping down as prime minister, Starmer said he would stay on as an MP until the next general election, which must take place by 2029.
In his statement on Tuesday, however, Starmer said he was ready to hand the seat to a successor.
Conservative chairman Kevin Hollinrake accused him of making "another U-turn having pledged to stay on", and said the decision would result in a "costly by-election for taxpayers".
Starmer's plans after leaving the Commons
Starmer has not said what specific international affairs role he may take up after leaving Parliament. Global issues and diplomacy were prominent during his time as prime minister.
In his departure interview in July, Starmer was asked whether he had another major political or international job in him. He replied: "I don't know is the honest answer to that."
Starmer's decision departs from the recent pattern of former prime ministers remaining in the Commons after leaving Downing Street, BBC reported.
Rishi Sunak remains the Conservative MP for Richmond and Northallerton two years after leaving No 10. His predecessor Liz Truss stayed on as a backbencher until she lost her seat to Labour at the 2024 general election.
Theresa May remained an MP for five years after leaving Downing Street.
Boris Johnson and David Cameron, however, both quit the Commons shortly afterwards.
