Guesde began his career as a radical journalist and in 1877 founded one of the first modern Socialist weeklies, L'Égalité. He consulted with Karl Marx and Paul Lafargue (a son-in-law of Marx) in 1880 on a socialist program for the French labour movement. Adopted by a national labour congress in 1880, the program called on workers to elect representatives sworn to “conduct the class struggle in the halls of parliament”; i.e., to stand uncompromisingly for the establishment of a socialist state. Guesde was opposed by members of the labour movement who were known as possibilists and who sought to win labour gains by economic and political pressure-group action. The possibilists advocated aggressive collective bargaining and strikes and argued that workingmen should vote for progressive political candidates regardless of their party affiliations.

A prolific author and powerful orator, Guesde served in the Chamber of Deputies beginning in 1893 and as minister without portfolio in 1914 and 1915.