Seymour engaged in mercantile pursuits in Brockport until 1872 when he moved to Sault Ste. Marie, Michigan where he engaged in the manufacture of reapers and subsequently in the manufacture of lumber and in agricultural pursuits. He was a member of the Michigan House of Representatives from Cheboygan District, 1880–1882 and a member of the Michigan Senate 1882–1884 (31st District) and 1886–1888 (30th District).