In 1894-95, Marx was the Detroit estimator-at-large. In 1895 he was elected as an alderman, a position he held for eight years. In 1904, Marx ran for City Treasurer, but was beaten. He served as a delegate to the Republican National Convention in 1908 (and was again a delegate to the Republican National Convention in 1916). In 1910, he was appointed City Assessor, and two years later saw his first term as Detroit's mayor. Marx served three terms in all as mayor.