Twenty-five-year-old Keir Mather will become the youngest MP in the Commons after overturning a 20,137 Tory majority in Selby and Ainsty.
The newly-crowned ‘Baby of the House’ secured a 4,161 majority in the North Yorkshire seat.
The swing from Conservative to Labour of 23.7 percentage points is the second-largest swing managed by Labour at a by-election since 1945.
A similar swing across the country would result in it winning more seats than in Tony Blair’s 1997 landslide, Labour claimed.
Labour leader Sir Keir Starmer said: “This is a historic result that shows that people are looking at Labour and seeing a changed party that is focused entirely on the priorities of working people with an ambitious, practical plan to deliver.
“Keir Mather will be a fantastic MP who will deliver the fresh start Selby and Ainsty deserves.
“It is clear just how powerful the demand for change is. Voters put their trust in us — many for the first time. After 13 years of Tory chaos, only Labour can give the country its hope, its optimism and its future back.”
Reaction was quick to flood in on social media, with some saying the result shows the Tories are “finished”.
Labour MP Karl Turner, meanwhile, said he had it put to him recently by a prominent former Tory MP that “if we lose Selby and Ainsty where under Boris in 2019 we won every single ballot box, we are truly f*cked in just over a years time”.
Related: Ministers given £455,000 in severance payments after year of political turmoil