ST.-JACUT-DE-LA-MER, France — The unmistakable candidate stood out during a campaign stop in a traditional Breton seaside village. “Ah, it’s you!” a middle-aged woman called out excitedly as he worked potential voters at the market — as if it could be anybody else.

Hervé Berville — tall, gaunt and of African descent — survived Rwanda’s genocide, was adopted by a Breton couple and studied at the London School of Economics. Just 27, he was snapped up last month by President Emmanuel Macron’s political movement, La République en Marche, to run for a seat in Parliament from this northwestern region.

Mr. Berville is the face of a new type of citizen-candidate in France, one with no political experience, no allegiance to the traditional parties and an undefined if firmly held belief that France needs to change. Surprisingly, polls before Sunday’s first round of national voting show that a majority of French voters may agree.

Candidates like Mr. Berville are part of a wave that Mr. Macron hopes will complete the thorough transformation of France’s political landscape. The young president has so far had few missteps, from the founding of his upstart nonparty movement 14 months ago to his upset election victory last month.