The former prime minister will step down as the MP for Holborn and St Pancras, and the Government has confirmed the appointment that will enable this departure from the House of Commons.
On Monday evening, the Chancellor of the Exchequer formally appointed Sir Keir Starmer to the position of Steward and Bailiff of the Chiltern Hundreds.
This appointment means he will not take up the equivalent post at the Manor of Northstead in Scarborough.
MPs wishing to leave Parliament before a general election must be appointed to such roles, as Commons rules prevent direct resignation.
A resolution dating from March 1624 stipulates that only death, disqualification, or expulsion can vacate a seat during a parliamentary session.
The mechanism is described as a legal fiction that permits members to work around the restriction on resignation.
In July, Reform UK leader Nigel Farage was appointed to the Northstead position after deciding to quit as an MP and seek to win back his seat.
Speaking to a local publication as he announced his departure, Sir Keir, who was first elected in 2015, indicated his intention to concentrate on international matters following his time in Downing Street.
He stated that he would focus on defence, security, trade, and technology in an era of rapid change.
He also mentioned his continued commitment to efforts against violence affecting women and girls, work he has pursued for an extended period alongside others.
He added that after serving as prime minister, it was appropriate to determine what would come next and that concentrating on international affairs represented the right course of action.