The Labour leader said the Irish border was “fundamental” and warned Boris Johnson against any move that “negotiated away” peace in Northern Ireland.
Mr Johnson returned to London on Thursday night after a round of talks with the French President and German Chancellor Angela Merkel aimed at convincing the pair to remove the backstop from the existing EU withdrawal agreement.
He has reportedly already ordered ministers to ramp up the search for viable “alternative arrangements” that can replace the backstop, which Brexiteers fear will leave the UK too closely aligned to the EU with little ability to influence its rules if it is triggered.
Speaking alongside the Prime Minister, Mr Macron said the controversial arrangement was “not just technical constraints or legal quibbling” but “genuine, indispensable guarantees” to preserve peace in Northern Ireland and the integrity of the single market.
Describing the backstop as “indispensable”, he added: “We will not find a new withdrawal agreement within 30 days that will be very different from the existing one.”
Asked about Mr Macron’s comments during a trip to Cumbria, Mr Corbyn said: “I agree with President Macron. The question of the Irish border is fundamental to a lot of things.
“The Irish peace process was an enormous step forward – it’s an international treaty, it’s an international agreement.
“It cannot be negotiated away by Boris Johnson or anybody else. “So, I think President Macron is quite right to say they’re not going to allow a hard border to return in Ireland and I’m absolutely with him on that.”
Mr Corbyn – who had used his trip to warn of the “carnage” a no-deal Brexit could cause to Britain’s farms – meanwhile hit out at the Prime Minister’s vow to leave the European Union “do or die” by 31 October.
The Hallowe’en deadline was handed to Theresa May by the EU, after Britain failed to exit the bloc by the original 29 March and then 12 April Brexit dates.
But the Labour leader said: “There’s no need for this 31 October deadline to be there.
“Boris Johnson could perfectly easily take much longer to negotiate, much longer to talk about it, listen to what other people are saying instead of holding this cudgel to everyone’s head saying, it’s got to be done by 31 October with all the damage that will do to our farming communities.”