Andy Burnham wins the election in Makerfield in northwest England, where he ran against Rob Kenyon from the right-wing populist Reform party.
Burnham, known as the "King of the North," is a popular politician in Manchester and has vowed to challenge his Labour colleague Keir Starmer for the party leadership and the role of Prime Minister - which requires a seat in parliament.
"We've been going in a direction for 40 years that simply hasn't worked for the people and places in this part of the world," Burnham told cheering supporters on Friday.
"Now is the time for change. We have an opportunity to turn things around," he said, promising to chart a new path for Britain.
"Last chance"
Burnham received almost 55 percent of the vote. Voter turnout was a historically high 59 percent.
If Starmer leaves office this year, Britain will have its seventh prime minister in ten years.
Dozens of MPs from within his own party have called for Keir Starmer to resign. Now, after Burnham's landslide victory, the pressure on the prime minister is likely to increase. According to polls, Burnham is Labour's most popular politician and would likely win a direct vote against Starmer among party members.
Starmer vows to fight
Keir Starmer reiterated on Friday his promise to fight if his party leadership is challenged.
If I am challenged, I will run, I will run. I have said repeatedly that I will not shy away from it.
Starmer has previously hinted that he would offer Burnham a ministerial position if he won in Makerfield.
Keir Starmer congratulated Burnham on Friday morning on X:
"Voters chose Labour’s campaign of hope and optimism over division and hatred," he wrote.
