In an emotional victory speech, Spencer promised to fight for those who feel “left behind”, as she celebrated a majority of more than 4,000.
This is the second by-election since Labour’s general election victory in 2024 and the party’s second loss to a party with only a handful of sitting MPs.
The poll was triggered by the resignation of former Labour health minister Andrew Gwynne, who was suspended from the parliamentary party for offensive WhatsApp messages a year ago.
The Greens’ victory at Gorton and Denton represents the sixth largest Labour majority to be overturned at a by-election since World War Two, in a seat that had been held by the party for nearly 100 years.
Spencer received 14,980 votes, nearly 41% of all votes cast, and there was a swing of 26.4% from Labour to Greens.
Reform UK’s Matt Goodwin came second with 10,578, while Labour’s Angeliki Stogia was third with 9,364. The Conservative Party’s Charlotte Cadden came fourth with 706 votes – the party’s worst ever by-election result – and the Liberal Democrats’ Jackie Pearcey had 653.
In her victory speech Spencer – who becomes the Green Party’s fifth MP – said: “Working hard used to get you something. It got you a house, a nice life, holidays, it got you somewhere.
“But now working hard, what does that get you? Because talk to anyone here and they will tell you, the people work hard but can’t put food on the table, can’t get their kids school uniforms, can’t put their heating on, can’t live off the pension they worked hard to save for, can’t even begin to dream about ever having a holiday, ever.
“Because life has changed. Instead of working for a nice life, we’re working to line the pockets of billionaires. We are being bled dry.”
Spencer, who is also a councillor in Trafford alongside her job, added: “Now to my customers, I’m sorry, but I think I might have to cancel the work that you had booked in, because I’m heading to Parliament.
“And when I get there, I will make space for everyone doing jobs like mine.”
Labour’s Angeliki Stogia came third in what was considered a safe Labour seat
This is a dismal result for Labour and will inevitably become part of the discussion in the party about Keir Starmer’s leadership.
The prime minister may well face criticism for the decision, on which he spent personal political capital, to block Andy Burnham from standing.
But what will probably be the most intense subject of debate within Labour will be the question of what this means the party’s political strategy should be going forwards.
One senior figure on the “soft” left of the Labour Party, a faction associated with figures like the former deputy prime minister Angela Rayner, said to me: “This must be the end of the McSweeney strategy of alienating our own voters.”
To translate: now that Morgan McSweeney, the prime minister’s chief of staff and main strategist, has left, Starmer should become more left wing.
Another striking element of the result is that actually Labour figures close to the campaign here in Manchester had been cautiously optimistic in recent days. They were wrong… by some distance.
One Labour MP said to me: “The campaign was great. But you can’t have an organisational solution to a leadership problem.”