At 17, Amine Kessaci found himself seated close to the president of France, Emmanuel Macron, who had come to Marseille to kick off his second presidential campaign in 2021.

Well-known for his top-down approach to policymaking, Mr. Macron described his plan to inject large amounts of state money into Marseille, France’s second-most populous city, with the goal of stimulating its economy and ending its rampant violence.

With the leader of France squeezed on a seat almost next to him, Mr. Kessaci, the son of Algerian immigrants, did not miss his chance for an impromptu audience. In a voice that was simultaneously calm and combative, he urged Mr. Macron to be more inclusive in his decision-making.

“There is no point to come with a plan from Paris drafted on a plane, or I don’t know where. You have to build it with us,” he told Mr. Macron, who did not respond to the substance of Mr. Kessaci’s comment, simply asking him his age and then slightly applauding.

Less than three years later, Mr. Kessaci (pronounced keh-ssah-see) ran for a National Assembly seat as a candidate of the Green Party, part of the left-wing New Popular Front coalition. He narrowly lost — by 835 votes — in the snap legislative elections in July to Gisèle Lelouis, 72, a member of the far-right National Rally party. The election resulted in a deadlock that has yet to be broken to form a government.