Macron, a 39-year-old former economy minister, was given little chance when he launched a new political movement "En Marche" (On the Move) last year ahead of a vote that was billed as a fight between conservatives and the far-right.
But the pro-European progressive is now a frontrunner to become France's next leader and will draw strength from an alliance with veteran centrist Francois Bayrou, who decided against mounting a rival presidential bid on Wednesday.
Explaining his decision to join forces with Macron, Bayrou yesterday said the two shared a rejection of the traditional French left-right political system.
"We just had the feeling that we could not go on as before," he said, adding that it was "no secret" that the two had had differences in the past but they had put them behind them.
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The 65-year-old veteran who finished third in the 2007 presidential election said: "My role is very simple -- I am here to help."
Environmentalist Yannick Jadot dropped out and threw his support behind Hamon, while Communist-backed Jean-Luc Melenchon said he was "open to discussion."
Polls show the three have enough supporters to mount a serious challenge together, which means a potential tie-up between the splintered leftist candidates could produce another upset.
While commentators said Bayrou gave Macron's campaign more substance, a poll by Tilder and OpinionWay for LCI television showed that 72 percent of voters believe the tie-up "changes nothing".
"It might be that we only see what's going to happen on the night of the election," veteran French political watcher Philippe Braud of Sciences Po university told AFP on Thursday.
Two new polls yesteday showed far-right leader Le Pen stretching her lead in the first round, where she would win 25-27.5 percent if it were held now.
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