The late-night deal means Britain will not crash out of the bloc on Friday and gives Mrs May more than the three months she had asked for to build a parliamentary majority behind the withdrawal treaty she negotiated with the European Union past year.
His tough position against a long extension, which sounded like "almost a veto" to some leaders, changed the atmosphere in the room.
European Council President Donald Tusk acknowledged as much when he delivered a message to Britain: "Please do not waste this time".
Irish premier Leo Varadkar has said that Britain should have "a say" in future trade if it is part of a customs union after leaving the EU.
She did not define precisely how long the expansion may be.
But during exchanges in the Commons, Mr Corbyn warned the Prime Minister she had to be prepared to compromise if the talks were to stand any chance of success.
The Prime Minister told MPs that it would still be possible for Britain to avoid the Euro-elections if Parliament reached agreement before the contests on 23 May.
Mrs May gave a one-hour presentation setting out her case for an extension to June 30, with a break clause allowing the United Kingdom to leave as soon as her Withdrawal Agreement was ratified.
It remains to be seen whether her pleas win anyone over.
Macron addressed the press at the end of the meeting, calling the conclusion the "best compromise possible", adding that the October 31 deadline "protects us", because it was "a key date, before the installation of the new European Commission".
But a few days of discussions have failed to make a breakthrough. Still, the negotiations are set to continue.
May is hoping to reach an agreement with Labour in order to approve her divorce deal, which has been rejected three times by parliament.
But the government has relaxed its contingency plans after European Union leaders on Thursday agreed to postpone the Brexit deadline to October 31, ending the possibility of a no-deal Brexit on April 12.
"The pressure on her to go will increase dramatically, I suspect, now".
That leaves her facing a second referendum.
May signaled she would take a longer extension, so long as it contained a trigger should Britain finish its Brexit impasse. The initiative for an election or for a referendum will most likely not come from the Prime Minister: it's the Parliament that has to lead the way forward. Frontrunners include Foreign Secretary Jeremy Hunt and his predecessor Boris Johnson, Environment Secretary Michael Gove and former Brexit Secretary Dominic Raab.
"It's no different to having a snap general election, and we've managed those perfectly well in the past".
What does 31 October mean?
"It probably has more to do with internal French politics", a German diplomatic source said.
Macron was happy to play hard ball to ensure that Britain doesn't disrupt the European Union on its way out the door.
Later on Thursday morning, French government spokesperson Sibeth Ndiaye told French TV station CNews that "it is not impossible that we could still have a no-deal Brexit".
But Parliament has voted repeatedly to rule out "no-deal", and even passed a law that forces the Government to ask for delay rather than crash out.
The bloc had already granted Britain a delay once from the original March 29 deadline.
"The EU retained its unity on Brexit - albeit only just", it said.
With one Brexit day gone and another following, the Government has lost control of the timetable. "Putting in danger the functioning of Europe is not preferable to your no-deal". The proposal is backed by many in Labour and other opposition parties, plus some of May's Conservatives.
"I make no apology for being clear".