He ran as a radical socialist in a by-election to replace Émile Dubois, who had died on 7 May 1904. Steeg was elected in the second round on 24 July 1904 for the second riding of the 14th arrondissement of Paris. As a new deputy, Steeg threw himself into a campaign for the protection and education of children. Steeg became a lawyer in Paris in 1905. He was re-elected with growing majorities in 1906 and 1910. In 1906 he was elected to the Budget Committee, responsible for Posts and Telegraphs. In 1907 he was appointed the rapporteur on the Public Education budget.