He regularly authored reviews for the Plans magazine, was co-founder of the journal Prélude, and Minister of Labour in the Vichy regime.
As a socialist activist, he attended meetings of the General Confederation of Labour (CGT) and was a contributor to the development of the revolutionary syndicalist movement in the years 1904–1908.
In 1910, disappointed with the evolution of the CGT, Lagardelle retired to Toulouse where he became responsible for the local chamber of commerce.
Like many other contemporary French revolutionary unionists, such as Gustave Hervé and Georges Valois, he left the labour movement and developed a tendency towards fascism.
Fascinated by Italian fascism, Lagardelle assisted the Ambassador of France to Rome, Henry de Jouvenel, from 1932 to 1937 in an attempt to establish a Franco-Italian alliance to prevent further German expansionism.