• "Keir Starmer - this is for Gaza," the former Labour MP said, after polling 12,335 votes, nearly 6,000 more than any other candidate.
• Labour had withdrawn support for candidate Azhar Ali over remarks widely alleged to be antisemitic.
George Galloway is back in Parliament with a resounding win in the Rochdale by-election after a campaign in which the Gaza war was a running theme.
"Keir Starmer - this is for Gaza," the former Labour MP said, after polling 12,335 votes, nearly 6,000 more than any other candidate.
Mr Galloway will take his Commons seat for the Workers Party of Britain.
Labour had withdrawn support for candidate Azhar Ali over remarks widely alleged to be antisemitic.
Mr Ali apologised for his remarks.
Mr Galloway has previously been an MP for Labour until 2003, then in the Commons as an independent and Respect Party MP for three constituencies between 2003 and 2015.
Smaller parties left the mainstream candidates in the dust in the Rochdale vote, which was sparked by the death of Labour MP Sir Tony Lloyd, with second place going to independent and local businessman Dave Tully.
In his victory speech, Mr Galloway highlighted the local voters' rejection of the two main parties in Westminster.
He said: "Keir Starmer and Rishi Sunak are two cheeks of the same backside and they both got well and truly spanked tonight here in Rochdale."
He was interrupted by a heckler accusing him of being a climate change denier, before she was shouted down by his supporters, and had orange confetti thrown over him by rival candidate Rev Mark Coleman, a Just Stop Oil supporter.
But none of this fazed the 69-year-old, who went on to warn that his former party would "pay a high price" for "enabling, encouraging and covering for the catastrophe" in Gaza.
Mr Galloway has long agitated for causes related to the Middle East, including for Palestinian rights, and has regularly stood for election in constituencies with a high Muslim population, such as Rochdale.
He told the BBC he had 60 Workers Party colleagues willing to stand in the general election and there would be "a shifting of the tectonic plates in scores of parliamentary constituencies".
"It's true that every Muslim is bitterly angry at Keir Starmer and his misnamed Labour party - but you would be very foolish if you didn't realise that millions of other citizens of our country are too," he said.
"Beginning here in the north west, in the west Midlands, in London, from Ilford to Bethnal Green and Bow, Labour is on notice that they have lost the confidence of millions of their voters who loyally and traditionally voted for them, generation after generation."
As well as pledging to save the town's football club from "extinction", Mr Galloway hailed the "remarkable achievement" of Mr Tully in coming second in the poll as an independent candidate campaigning on local issues.
Mr Tully, who got 6,638 votes, is well-known in Rochdale as he runs a garage business and is involved with the town's rugby club.
The Conservative candidate Paul Ellison came in third place with 3,731 votes, the suspended Labour candidate Azhar Ali in fourth with 2,402, and Iain Donaldson came fifth for the Liberal Democrats with 2,164.
The Reform Party had hopes this by-election could be a breakthrough for them as they fielded Simon Danczuk, the former Labour MP for Rochdale, but he was beaten into sixth place with 1,968 votes.
Mr Galloway's party was only formed in 2019 and because it therefore did not field a candidate in Rochdale in the general election, Mr Galloway recorded a historic 41% swing against Labour in the vote.
He also told the BBC afterwards that he had achieved political history in another way, matching Winston Churchill as the only MP to represent four separate towns and cities in the House of Commons.
Galloway's constituencies
- 1987 - 2005: MP for Glasgow Kelvin and Hillhead, Labour, independent, and Respect Party
- 2005 - 2010: MP for Bethnal Green and Bow, Respect Party
- 2012 - 2015: MP for Bradford West, Respect Party
- 2024: MP for Rochdale, Workers Party of Britain
Labour's deputy national campaign coordinator Ellie Reeves said Mr Galloway was only able to win as Labour did not stand a candidate, which she said was the right decision under "unique circumstances".
She said Mr Galloway "stokes up division" in communities, and that Labour's position on calling for an immediate humanitarian ceasefire in Gaza was clear adding that "crucially we also need to make a two-state solution a reality".
She pledged to select a new candidate for the general election who would be able to "unite communities".
Former Rochdale Labour council leader Alan Brett told BBC Radio 4's Today programme he didn't think Mr Galloway would have won if the Labour party's selection process hadn't been mishandled.
He added: "I don't think he's for Rochdale - I think he's for himself - I don't think he cares about Rochdale."
The Campaign Against Antisemitism (CAA) said it was "extremely concerned" by Mr Galloway's victory, accusing him of having an "atrocious record of baiting the Jewish community", including calling for Bradford, when he was an MP there, to be declared an "Israel-free zone".
His victory comes amid concerns the war in the Middle East is inflaming community tensions in the UK, fuelling a rise in hate crimes and leading to MPs reporting that threats have been made personally against them.
Veteran political pollster Sir John Curtice told the BBC the Rochdale result will intensify pressure on Sir Keir Starmer to toughen up Labour's stance on Israel.
However he doubted there would be much impact on the general election result, because it's "unlikely that anybody else has the ability to... exploit this issue [the war in Gaza] in the way that Mr Galloway is uniquely able to".
John McTernan, Tony Blair's former director of political operations, said the Rochdale result was a judgement on Parliament's inability to come to a position on a Gaza ceasefire.
Speaking on Today he says the Labour party "messed up" their selection in Rochdale because they were rushing to counter the "momentum" of Mr Galloway's campaign.