Echoing comments by German Chancellor Angela Merkel, Macron supported allowing another month to find a solution to the vexed issue of the Irish border which has bedevilled negotiations since 2017.
But he also said the so-called Irish backstop that has caused such controversy in London was "indispensable" and said all talks had to be based on the withdrawal deal negotiated by Johnson's predecessor Theresa May repeatedly rejected by the British parliament.
"We need to try to have a useful month," Macron said alongside Johnson, adding that France was nonetheless planning for all scenarios and "notably that of no-deal" when Britain exits the EU on October 31.
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Johnson, whose pictures showed putting his foot on a table in the Elysee palace, however, insisted that solutions were "readily available" to prevent checkpoints returning in divided Ireland.
Macron admitted he had a reputation as the "hardest in the gang" on Brexit and rejected Johnson's calls to scrap the backstop arrangement for Ireland.
The backstop is a provision guaranteeing that border checks will not return between EU member Ireland and Northern Ireland which is part of Britain.
The backstop provided "indispensable guarantees to preserve stability in Ireland and the integrity of the single market," Macron said.
Johnson wants the backstop removed and has called it "anti-democratic" because it will require London to keep its regulations aligned with the EU during a transitional period when the country is no longer a member of the bloc.
A senior EU official in Brussels told reporters on Thursday ahead of the talks in Paris that the European side was "a little concerned based on what we heard" on Wednesday from Johnson in Berlin.
Since Johnson's ascent to power last month, the chances have risen of a "no deal" Brexit on October 31, which economists see as likely to wreak economic damage on Britain and the EU.
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"The EU and member states need to take the possibility of a 'no deal' outcome much more seriously than before," the EU official said on condition of anonymity.
A French official said on Wednesday that this was becoming the "most likely" scenario.
But the window offered by France and Germany to Johnson to find a solution led to renewed optimism in financial markets, where the pound rose by as much as 1.0 per cent against the euro and dollar.
"Let's get Brexit done, let's get it done sensibly and pragmatically in the interests of both sides," said Johnson.
He said all the necessary work should be done "to make sure - whether we get an agreement or not - our exit is as smooth and pain-free as possible."
Speaking in the Netherlands later on Thursday, Merkel said Britain had right up to the current deadline for Brexit of October 31 to find a solution to the Irish border problem, beyond the 30-day window she mentioned on Wednesday.
Johnson said that he had been "powerfully encouraged" by his talks with Germany's leader. "I admire that 'can do' spirit that she seemed to have," he said.
UK to hold Brexit talks with Macron after Merkel offers glimmer of hope
But many Brexit watchers saw Merkel's remarks as fitting a pattern in which Merkel has often been more conciliatory in public about Brexit than Macron, whose abrasive remarks have angered London in the past.
"There is not the width of cigarette paper between Paris and Berlin on these issues," a senior aide to Macron said on Wednesday on condition of anonymity.
Mujtaba Rahman, Europe managing director for the Eurasia Group consultancy, interpreted the offer of talks as a minor concession designed to avoid the EU being seen as being responsible for a "no deal" Brexit.
"They're saying to Boris, you insist this can be done another way. You have 30 days to produce what you, the British, could not produce in two years," he wrote on Twitter.
Johnson has staked his leadership on withdrawing Britain from the EU by the current deadline "do or die".
Some analysts see a risk of relations between Macron and him becoming stormy in public, but the two men smiled and slapped each other on the back as they appeared on the steps of a sun-lit Elysee palace and at the end of two hours of talks.
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