Nigel Farage has said he will not be standing as a candidate in the general election on 12 December.
The Brexit Party leader told the BBC's Andrew Marr he had thought "very hard" but had decided he could "serve the cause better" by supporting his party's 600 candidates "across the UK".
"I don't want to be in politics for the rest of my life," he said.
Jeremy Corbyn said Mr Farage's decision was "a bit weird" given the Brexit Party hopes to stand in most places.
The Labour leader said: "It's obviously his decision. It's a bit weird to lead a political party that is apparently contesting all or most of the seats up in the election and he himself is not offering himself for election."
Mr Farage, who has stood unsuccessfully for Parliament seven times and currently sits in the European Parliament, also also criticised the PM's Brexit deal..
The 55-year-old told BBC One's Andrew Marr Show the deal agreed earlier this month was "virtually worse that being in the EU".
"If Boris Johnson was going for a genuine Brexit, we wouldn't need to fight against him in this election," he said.
On Friday, the prime minister rejected an alliance with Mr Farage's Brexit Party, telling BBC political editor Laura Kuenssberg doing deals with "any other party... simply risks putting Jeremy Corbyn into Number 10".
Mr Farage had called on the prime minister to drop his Brexit deal, unite in a "Leave alliance" or face a Brexit Party candidate in every seat in the election.
He told the Marr show: "I always thought that to win an election, get a big majority so we can get a proper Brexit, a coming-together would be the objective.
"I still hope and pray it happens but it doesn't look like it will."
Mr Johnson maintains that the only way out of the EU is to "go with the deal we've got".
The prime minister told Sophy Ridge on Sky that he was "deeply, deeply disappointed" to miss the 31 October deadline to secure Brexit, calling it "a matter of deep regret".
The PM had previously said he would rather "die in a ditch" than ask the EU to delay Brexit beyond Halloween.
Mr Johnson told the programme that he was sorry, and took responsibility, for missing the date, but accused Parliament of failing to implement his deal.
He also said Donald Trump was "patently in error" when the US president warned the government's Brexit deal would hamper a UK-US trade deal.
Mr Farage said Mr Johnson's deal "kills off any chance of genuine independence".
"If Boris is determined to stick to this new EU treaty, then that is not Brexit," he said.
Analysis: Why is Farage not standing again?
By political correspondent Jessica Parker
Political opponents of Nigel Farage will accuse him of running scared after he said he would not stand as a candidate in December's poll.
They will suggest he's not going to run because he thinks he's not going to win.
But the flip side is that rather than concentrating on one constituency where he personally might try to win, Mr Farage is making it clear he's going to try to make Boris Johnson's life pretty difficult.
That's if this so-called Leave alliance doesn't happen - and it doesn't look like it will.
The Brexit Party leader has made it clear he has no interest in getting on board with Mr Johnson's deal at all.
It's likely Mr Farage will spend a lot of the campaign really criticising it, whereas the Tory party leader will say he's got an oven-ready deal to present and get through Parliament within weeks.
Treasury minister Rishi Sunak hit back at the criticism of the deal, telling the Andrew Marr show: "I campaigned for Leave, I spent a lot of time talking to my constituents and others across the North East and in Yorkshire - what do they want from Brexit?
"They want to end free movement and replace it with a points system, they want to end the fact that money keeps going to the EU year after year, they want to make sure we're in control of our laws, and also they want us to have an independent trade policy. These are all things the prime minister's deal delivers.
"What I would say to Nigel Farage is, sometimes in politics, as in life, you've got to take yes for an answer."
Also appearing on the programme, shadow chancellor John McDonnell suggested that a Labour government would seek to end privatised contracts in the NHS.
He said that, as the contracts ran out, the work should be brought in-house, and that the public didn't want money "being poured into the pockets of profiteers".
Pushed on whether an incoming Labour government would see the eradication of all privatisation in the NHS, Mr McDonnell said "we'll see how those contracts run out."
The Conservatives have strongly denied that the NHS is "up for sale".
Asked if Labour would scrap the expansion of Heathrow airport, Mr McDonnell said the party would make the decision based on a set of criteria covering the environmental, economic and social impact of the project.
"On the current criteria, we've said very clearly, Heathrow expansion doesn't qualify."
And on taxes, he said Labour would increase income tax for the top 5% of earners and raise corporation tax in order to pay for "investments in schools and training".