Starmer leaves the Commons six weeks after Downing Street, forcing a Holborn by-election

Keir Starmer told his local paper on Tuesday that he is leaving the House of Commons. The announcement came six weeks after he resigned as prime minister and hours before Andy Burnham, who replaced him in July, made his first appearance in the chamber as the new occupant of No. 10.

Starmer has sat for Holborn and St Pancras since 2015. In July he told the BBC he would remain an MP until the next general election, which is not due until 2029. On 1 September he reversed that. "It has been a huge honour and privilege to represent the best constituency in the country," he told the Camden New Journal. "I will now focus on other things and that will be international affairs including defence, security, trade and technology in a fast-changing world."

He confirmed the decision in a post on X. He also said he would keep working on violence against women and girls, a file he took up before he entered Parliament.

From landslide to exit in two years

Starmer led Labour from its 2019 result, the party's worst since 1935, to the 2024 landslide that ended 14 years of Conservative government. That majority did not last as political capital. U-turns, spending cuts, a diplomatic row, pressure from Reform UK and a challenge from Burnham wore down his standing among Labour MPs. Local election results in 2026 finished the argument. He left Downing Street in July. Burnham became Britain's seventh prime minister in a decade.

The timing of the Commons resignation is pointed. Starmer chose the morning of Burnham's first day back in the House. Labour's current leader issued a statement praising the 2024 victory and wishing Starmer's family well. The courtesy does not hide the fact that a sitting former prime minister departing mid-term forces a by-election on the government that replaced him.

A safe seat that is no longer quiet

Holborn and St Pancras has been a Labour seat for decades. Starmer's 2024 majority was just over 11,500. An independent who campaigned against Israel's war in Gaza took nearly 19 percent of the vote in that election. That share is the number Burnham's organisers will watch. A by-election in inner London, with Gaza still a live issue and Reform UK hunting protest votes, is a different contest from a general election night.

No date has been set. The newspaper report did not give a timetable. Once Starmer formally vacates the seat, the writ will follow the usual Commons process. Turnout and the identity of Labour's candidate will matter more than the party's national poll bounce under Burnham, which has been visible but untested in an actual ballot.

The international file he wants

Foreign policy was often treated as Starmer's stronger suit while he was in office. He now says that is where he will spend his time: defence, security, trade and technology. He has not named an institution, a government or a private employer. David Cameron and Tony Blair also left the Commons soon after leaving No. 10. Blair built a commercial and diplomatic network. Cameron later returned as foreign secretary. Starmer has not said which model he prefers.

Violence against women and girls is the other thread he named. That work predates his election in 2015 and gives him a domestic subject that does not require a whip's office. It also keeps him in public view in a field where Labour still claims ownership.

The immediate consequence sits in Camden, not in any future international post. A former prime minister who promised to stay has left. The government that pushed him out now has to defend his old majority. That is the first hard number attached to Burnham's premiership.