Andy Burnham will make a bid to return to the Commons as an MP after Wes Streeting's resignation as health secretary heaped pressure on the prime minister.
The Greater Manchester mayor said he would seek the Labour nomination in Makerfield after MP Josh Simons said he would step down to make way for him.
Any candidate in a Labour leadership contest to replace Sir Keir Starmer must be an MP, meaning Burnham could potentially trigger a leadership challenge.
Streeting, who said he had lost confidence in the prime minister's leadership, called for a broad debate about the party's future but stopped short of confirming if he would stand for leader himself.
Announcing his resignation, Simons said Burnham could “drive the change our country is crying out for”.
Burnham said he would seek people's support to return to Parliament in order to "bring the change we have brought to Greater Manchester to the whole of the UK and make politics work properly for people".
He would, he added, "not take a single vote for granted" and would "work hard to regain the trust of people" in the north-west constituency, which Labour held in 2024 with a majority of 5,399 votes over Reform UK.