Seanor was born in 1833 in Boston, Massachusetts. He was living in New York when he joined the Navy. He served during the Civil War as a master-at-arms on the . Although their enlistments had expired, Seanor and crewmate Andrew Jones voluntarily transferred to the to fight in the Battle of Mobile Bay on August 5, 1864. During the battle they "carried out [their] duties gallantly" according to the Medal of Honor citation. For this action, both Seanor and Jones were awarded the Medal of Honor four months later on December 31, 1864.