 He was assistant corporation counsel of Detroit from 1903 to 1907 and city comptroller 1907-1910.In 1910, Doremus defeated incumbent Republican Edwin C. Denby to be elected as a Democrat from Michigan's 1st congressional district to the Sixty-second and to the four succeeding Congresses, serving from March 4, 1911 to March 3, 1921, and was elected chair of the Democratic Congressional Campaign Committee in 1913.He was a delegate to Democratic National Convention from Michigan in 1916 and 1920.