Steeg entered French politics in 1904 as a radical socialist, although his views were generally moderate. He was a Deputy of the Seine from 1904 to 1914 and Senator from 1914 to 1944. At different times he was Minister of Higher Education, Interior, Justice and Colonies. In the 1920s he was in charge of the colonial administrations first of Algeria and then of Morocco. He encouraged irrigation projects to provide land for French "colons" at a time of growing demands for political and economic rights from the indigenous people, accompanied by growing unrest. Steeg was briefly prime minister in 1930–1931.