Damien Tarel, a 28-year-old medieval history enthusiast, has been in custody since the assault on Tuesday which a prosecutor at the hearing called “absolutely unacceptable” and “an act of deliberate violence”.

Tarel was placed under arrest following the verdict from the court in the southern city of Valence and will spend the night in jail as he begins his sentence.

In its verdict, the court followed a recommendation from prosecutors for an 18-month sentence, but said he should serve only four, after a fast-track hearing.

Tarel had risked a maximum three-year jail sentence and a fine of €45,000.

Under French law, prison sentences of less than two years can be converted into non-custodial punishment.

The long-haired history buff and board games enthusiast told investigators that he “acted instinctively and without thinking” after waiting for Macron outside a school in the village of Tain-l’Hermitage.

In court, he expressed sympathy for the anti-government “yellow vest” movement and said that he and two friends had considered throwing an egg or a cream pie at the head of state during his visit to the Drome region, according to the BFM news channel.

“Macron represents the decline of our country,” he told the court.

Tarel, unemployed and living on benefits, said he had been annoyed by Macron’s decision to come to greet him – “an electoral tactic that I didn’t appreciate”, BFM reported.

In a video of the incident, a smiling Macron can be seen striding towards a crowd of onlookers including Tarel who are being kept behind a barrier.

Macron has shrugged off the assault, calling it an “isolated event”, and he has vowed to continue meeting voters despite concerns for his personal security.

Asked about it again during an interview on Thursday with BFM, he called it a “stupid, violent act” and suggested it was a consequence of the poisonous atmosphere found on social media.

“You get used to the hatred on social media that becomes normalised,” he said. “And then when you’re face-to-face with someone, you think it’s the same thing. That’s unacceptable.”

Leaders across the political spectrum have united in condemning the slap, with many seeing it as a symptom of the fraught political climate and declining standards of public debate just weeks from regional elections and 10 months from presidential polls.