Former Labour MP Ivan Lewis has urged people in Bury South, where he is an independent candidate, to vote for the Tory rather than himself to "stop Corbyn".
In a surprise move, Mr Lewis wrote on Facebook that it was "is the right thing to do" to back Conservative candidate Christian Wakeford.
"Many will be voting Conservative for the first time and it will require much soul searching. But it is the right thing to do," he said.
It comes after a YouGov poll suggested Mr Lewis had little chance of winning his old seat, which he represented from 1997 until this year, and forecast a Conservative victory.
He wrote on Facebook: “It has been a tremendous honour to represent my hometown for the past 22 years.
"In this election, I have spoken to many Bury South voters who have told me the priority for our local community and country is to stop Jeremy Corbyn becoming Prime Minister.
"As the Independent Candidate, I am grateful for the support I have received but it is now clear that the best way to stop Corbyn in Bury South is to vote Conservative and support their candidate Christian Wakeford.
“So today, I’m asking the thousands of voters in Bury South who don’t think Corbyn is fit to be Prime Minister to vote Conservative."
When Mr Lewis left Labour last year, he attacked Mr Corbyn's hostility to Israel, saying the Labour leader should be "honest and acknowledge your preference is that there should only be a state of Palestine".
Mr Lewis, who served as International Development Minister under Gordon Brown, was suspended from the party in 2017 over allegations of sexual harassment.
In his letter of resignation, he said he had "made it clear" to the party he was considering resigning, prompting the party's disciplinary body – the National Constitution Committee (NCC) – to move the case against him forward.
His letter to Mr Corbyn said: "This followed political control of the NCC passing to your supporters. This is a process which is flawed and subject to political manipulation.
"I have made it clear that I strongly refute the charges which have been made and I am willing to co-operate with a truly independent process."
He claimed to have seen emails sent in April that showed party authorities were not moving his case forward "for political reasons".