 He was a member of the New York State Senate from 1915 to 1925, sitting in the 138th, 139th, 140th, 141st (all four 13th D.), 142nd, 143rd, 144th, 145th, 146th, 147th and 148th New York State Legislatures (all seven 12th D.); and was Minority Leader from 1920 to 1922; Temporary President of the State Senate from 1923 to 1924; and Minority Leader again in 1925.In the Senate he strongly opposed Prohibition.After his years in the Senate, Walker set his sights on the 1925 election for Mayor of New York.