Former Prime Minister Sir Keir Starmer is stepping down as the Member of Parliament for Holborn and St Pancras, triggering an immediate by-election in his London constituency.

His departure from Parliament comes shortly after he was ousted as Labour leader and Prime Minister by Andy Burnham. It marks a swift end to Sir Keir's time in the House of Commons, coming on the heels of major political upheaval at the very top of government.

Speaking directly to the Camden New Journal, Sir Keir explained that he felt it was the "right time" to step away from the green benches. He originally took over the central London constituency back in 2015 from Frank Dobson, who was a prominent local MP and a member of the last Labour government.

Reflecting on his decade representing the area, Sir Keir said: "It has been a huge honour and privilege to represent the best constituency in the country and to have taken over from Frank Dobson, who was such a great constituency MP and a member of the last Labour government."

As he prepares for life outside the Commons, the former Director of Public Prosecutions outlined the new priorities that will occupy his time. He announced that he intends to dedicate his post-parliamentary career to international affairs, with a particular focus on global defence, security, trade, and technology.

As Sir Keir told the local paper: "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 made clear that this broad policy area will form one of the primary pillars of his future work.

Alongside international policy, Sir Keir stated he will maintain his long-standing work on domestic social issues. "I will also continue, as I have done for a long time now with others, work on combating violence against women and girls; that is an issue that matters to me hugely," he explained. "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."

Sir Keir's path through Westminster moved quickly after he was first elected in 2015. Prior to entering Parliament, he served as the Director of Public Prosecutions, and he was said to have been earmarked for the role of Attorney General had Labour won that general election. He subsequently served in Jeremy Corbyn's shadow cabinet, eventually succeeding Corbyn as Labour leader following the party's 2019 defeat.

Sir Keir went on to lead Labour to a landslide victory in the 2024 general election. However, his personal approval ratings subsequently nosedived, and heavy losses to Reform UK in Red Wall seats during local elections sparked growing calls for him to quit.

With Sir Keir now stepping aside, attention turns to his successor, Prime Minister Andy Burnham, who is scheduled to deliver his first speech to the House of Commons on Tuesday. At the same time, political parties will begin preparing for the contest to fill the newly vacated seat in London.

The precise timetable for the by-election in Holborn and St Pancras has not yet been confirmed, and we do not yet know who will stand to replace him. I'll be following this one.