 At the time of his death, he was the senior partner is the law firm of Osborn, Fleming & Whittlesey located at 20 Exchange Place.He also served as director of his mother's family business, Phelps Dodge, as well as the Chicago, Milwaukee, St. Paul and Pacific Railroad the Picacho Mining Corporation, the Tucson, Cornelia & Gila Bend Railroad Company, the Detroit, Toledo and Ironton Railroad, and was the chairman of the executive board of the Texas and Pacific Railroad.Osborn unsuccessfully ran for New York State Senate in 1894 and 1904 as an Independent Democrat, and sought the governorship in New York in 1918.