Ian Austin, a prominent critic of the Labour leader, made the remarks just hours after the party’s deputy leader, Tom Watson, announced he was quitting frontline politics at the December election.
Mr Austin, a former minister and adviser to Gordon Brown, also said he would be stepping down from parliament, as he cited antisemitism allegations that he claimed had “poisoned” the party under Mr Corbyn’s leadership.
He told BBC Radio 4’s Today programme: “I’ve got to be honest with people. I’m not going to run at this election.
“The country faces a big choice. There are only two people who can be prime minister on 13 December: Jeremy Corbyn or Boris Johnson and I think Jeremy Corbyn is completely unfit to lead our country, completely unfit to lead the Labour Party.
“It’s really come to something when I tell decent, traditional, patriotic Labour voters that they should be voting for Boris Johnson at this election. I can’t believe it’s come to this, but that’s where we are.”
Mr Austin, the MP for Dudley since 2005, resigned from the Labour Party in February, hitting out at Mr Corbyn for “creating a culture of extremism and intolerance”.
Speaking on Thursday – the second day of the official election campaign – Mr Austin added: “Look, the public has to make this choice. The British people have to decide this. Lots of traditional Labour voters are going to be grappling with this question.
“If they’ve got to face up to that, then I don’t think people like me should have the luxury of running away from it. What Jeremy Corbyn has done to the Labour Party, I don’t want him to be able to do that to the country.”
His remarks comes after the Labour veteran and deputy leader Mr Watson said he was giving up frontline politics after almost four decades to campaign on public health matters, staying on in his role until 12 December election.
Mr Watson said he was standing down for “personal, not political” reasons, and made no mention of the botched attempt the left to abolish his post on the eve of Labour’s conference in September.
“If he felt that the pendulum was about to swing back very rapidly the other way, then he might have hung on,” said one Labour MP. “Perhaps he thought the road ahead was a long, not a short one.”