"Of course the door is always open as long as the negotiations on Brexit have not finished," Macron said in a press conference.
But he stressed too that he respected the sovereign decision of the British people to leave the EU in their referendum a year ago, adding that the start of talks was an important milestone.
"We need to be clear and organised and once it (the Brexit process) has started we need to be collectively clear that it's more difficult to reverse course," he said at the Elysee palace.
Macron's comments echoed others by German Finance Minister Wolfgang Schaeuble on Tuesday.
"If they wanted to change their decision, of course they would find open doors, but I think it's not very likely," Schaeuble told Bloomberg Television.
May repeated her plans to stick to her timetable of starting discussions next week despite ongoing negotiations to form a government.
"I think there's a unity of purpose among people in the UK. It's a unity of purpose having voted to leave the EU that their government gets on with that and makes a success of it," she said.
May said the process would lead to "an arrangement for Brexit which will be the interests of the United Kingdom and the remaining 27 members of the EU."
After the talks, May and Macron also announced a joint action plan to tackle online extremism which aims to increase the pressure on internet giants and social media companies to tackle terror propaganda and hate speech.
It includes exploring the creation of new laws that would impose penalties on internet companies if they failed to act.
(Except for the headline, this story has not been edited by NDTV staff and is published from a syndicated feed.)
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