At the farm show in Châlons-en-Champagne, northern France, people climbed on tables and trampled flower beds to see him. Relaxed and wearing a suit to match his blue eyes, Emmanuel Macron posed for selfies, worked the crowd and savoured the excitement. “Macron président!” his fans chanted.

The visit to Champagne on 1 September opened what is a campaign for the French presidency in all but name. Two days earlier, the 38-year-old presidential protégé had quit the economy ministry, which he had led for two years, and embarked on a self-appointed mission to “transform” France.

Elsewhere, “Macron-mania” would be unthinkable. In other places, power is reached by ascending party ladders in internal elections. Macron, an eloquent fonctionnaire given a staff job at the Élysée Palace in 2012, is not a member of President François Hollande’s Parti Socialiste and has never been voted into office. But in France, the anointment of the monarchical president is personal: it is a meeting between “one man and the people”, as Charles de Gaulle said of the system tailored for him over half a century ago.

Macron, who was largely unknown to the public until August 2014, believes that the planets are aligned in his favour in the lead-up to next spring’s two-round election. France is in crisis, politics is discredited and the ruling left-wing establishment is a “dead star”, as he puts it. He is convinced that he can rally the middle ground with a vision of an outward-looking France, freed from the stifling orthodoxies of both left and right.

He could be right. A recent Odoxa survey ranked Macron second among potential presidential candidates after Alain Juppé (the 71-year-old centre-right front-runner). Hollande trailed in a crowded field that also includes Marine Le Pen of the Front National and the previous incumbent Nicolas Sarkozy.

Macron, whose career has included a stint with the Rothschild investment bank, sensed an opening when the media latched on to his impertinent style and the business world was impressed by his embrace of the market. To the anger of the conventional left, he promoted deregulation and championed entrepreneurship. There was further outrage when he said that there should be “young French people who want to be billionaires”. Such Tony Blair-style rhetoric is still unsettling for those who subscribe to what Macron calls the “traditional left-wing ideology that doesn’t allow for thinking about reality”.

Hollande’s apprentice abandoned him in April when he launched a political movement called En Marche! and set his sights on his master’s job. Fifty thousand people signed up as Macron, schooled in philosophy and an accomplished pianist, stirred crowds with visions of a France reborn. In Orléans in May, he identified himself with Joan of Arc, the symbol of French redemption. Hollande failed to rein in his insubordinate junior after Macron appeared with his wife, Brigitte – 24 years his senior – on the cover of Paris Match, which gushed about his supposed path to power.

Macron’s departure from the cabinet caused an uproar, and the leading TV channel TF1 broadcast a 25-minute interview with him on the evening news. He talked like a contender but refused to declare his candidacy. “I have touched the limits of our system, the last-minute compromises, its imperfect solutions,” he said.

Defining himself now as a progressive on the left, Macron is under fire from all sides except the small, centrist parties and dissident Socialists who back his independent run. Former colleagues are voicing contempt for “the traitor”. Manuel Valls, the French prime minister, calls him “Emmanuel Microbe” and Michel Sapin, the finance minister, dismissed him as “a firefly”. Sarkozy and Juppé mock him for disowning the work of his own ministry – as he did recently, when he said that the government’s reforms were only half-measures.

For commentators, Macron is good entertainment. The son of a doctor and a neurology professor, he was born in Amiens, northern France. His arrival in a field of political dinosaurs has brightened a dreary election campaign. Yet his party is small and he has yet to raise the millions of euros needed to run a campaign. “On paper, his ambition is pure madness. His chances of winning are minute,” wrote Cécile Cornudet of Les Échos, the business daily.

And his appeal is narrow. Macron is admired by urban, educated voters who despair of France’s archaic politics. His biggest support comes from older, centre-right voters who otherwise favour Juppé. Yet few have written him off. Gérard Collomb, the Socialist mayor of Lyons, who is his most influential backer, says that a hundred MPs, senators and mayors will rally to him. Jean Arthuis, a centrist who served as a minister under Jacques Chirac from 1995-97, said that there was hope in Macron’s “message of liberalism and social generosity”.

His plan is to edge out the old guard in the first-round election in April. That could demand just 18 per cent of the vote. If his chief rivals are the divisive Sarkozy and the enfeebled Hollande, this is possible. He could win a run-off against Le Pen, who is still deemed unelectable by mainstream voters.

The victory of a man who was unknown before 2014 would be stunning, says Christophe Barbier, the editor of L’Express magazine. “It would be a quasi-revolutionary phenomenon like France has not seen since . . . Napoleon Bonaparte.”