He was a leader in the pro-Nazi youth movement during the Vichy wartime years, but after prison time built a major newspaper empire and engaged in conservative politics.
Initially involved with the Socialist Youth movement in 1935, Robert Hersant founded the rightist political party Jeune Front in the summer 1940.
In 1941–1942, he created a camp in Brévannes, named after the Marshal Philippe Pétain to indoctrinate young people in the Révolution nationale ideology.
After launching a few unsuccessful publications, (Bazars et Galeries, l'Equipement Ménager, le Quincailler), in 1950, he started L'Auto-Journal, which met success due to the increasing popularity of automobiles.
In February 1953, he was elected mayor of Ravenel, Oise, and in January 1956 he ran for a deputy seat in the Assemblée Nationale as a radical candidate.
He was elected with the support of French Section of the Workers' International (SFIO) and Democratic and Socialist Union of the Resistance (UDSR).
It would have permitted the direct election of the Président du Conseil, and would have obliged him to form his cabinet from personalities that did not belong to legislative bodies.
He gradually built his empire by buying or creating local or regional newspapers through his holding company Socpresse (and its associate France-Antilles).
In 1975, he purchased from Jean Prouvost the great conservative newspaper le Figaro (with the help of Pierre Juillet and Marie-France Garaud, then adviser of Jacques Chirac), in 1976 the popular daily France-Soir, and in 1980 acquired "L'Aurore" from the estate of Marcel Boussac.
At the time, it was rumored that president Giscard d'Estaing had facilitated the obtaining of loans by Hersant in order to have the three Parisian newspapers (totalling 1.06 million in circulation) controlled by a political ally.