The ex-international development secretary said her concerns that the Tory Party was morphing into Nigel Farage’s Brexit Party had “come to pass”, and said that the Prime Minister was offering the country a “lose-lose” situation by threatening a general election.
The second referendum supporter and Conservative Party rebel told BBC Radio 4’s Today programme: “I will not be standing as a Conservative candidate at the next election.”
“I want to focus on making a difference on the ground on social mobility and I believe I can do that better outside Parliament than inside Parliament. We have seen Parliament gridlocked by Brexit.
“I will continue to represent my community, that heavily voted to remain, on Brexit. I have no doubt that the person following me will also represent our community on Brexit.”
During a speech outside Downing Street on Monday evening, Mr Johnson said he did not want a general election, but sources afterwards briefed that an October 14 poll could be on the cards if opposition and rebel Tories voted to block a no-deal Brexit this week.
Ms Greening said: “I don’t believe that the Conservative Party will offer people a sensible choice at the next election in respect of the fact that Boris Johnson is going to offer people a general election that faces them with the choice of a no-deal or Jeremy Corbyn.
“That is a lose-lose general election for Britain."
The former Cabinet minister said a “far better way” of resolving the situation was to offer a referendum on the “different options for Brexit” instead of a “messy” election that she predicted would be “yet again, inconclusive on a way forward on Brexit”.
The Putney MP said her party was “narrowing down its appeal” – a move, she suggested, that had been highlighted by the threat this week to long-serving MPs who would have the whip removed if they voted against the Government on Brexit.
Ms Greening said the threat had not worked on her and that she would be voting for legislation this week to force the PM to extend Article 50 rather than take Britain out without a deal.
“A job of an MP for me is to be Putney’s voice in Parliament,” said Ms Greening, who represents a Remain-voting constituency.
“That’s certainly what I have sought to do and I will do that today in making sure we pass this Bill hopefully through Parliament on Wednesday.
“My concerns about the Conservative Party becoming the Brexit Party, in effect, have come to pass and my decision is that if I really want to make a difference on the ground and on social mobility, then I need to do that outside Parliament. That’s what I’m prepared to do.”
Ms Greening said she would continue to be a Tory member and vowed to stay involved in politics, but said Parliament had been “stymied” by Brexit.
She added: “I want to focus on making a difference on the ground on social mobility and I believe I can do that better outside Parliament than inside Parliament. We have seen Parliament gridlocked by Brexit.”
It comes days after former Tory minister Richard Harrington announced he will also stand down at the next general election.
The MP for Watford has been a vocal critic of both Boris Johnson and Theresa May’s Brexit strategy.