Seymour was born on 12 January 1919 in New York, USA to Hungarian born Salomon and Mary nee Wolkenfeld and had a brother Harry and sister Phyllis.

Seymour worked as an accountant before he enlisted in Canada in 1940. He was assigned to 133 (Eagle) Squadron based at Biggin Hill.

He was the pilot of Spitfire EP167 when he was killed in an accident at Sharnden Farm, Sussex. He was initially buried at Brookwood Cemetery before his body was repatriated to Saddle Brook Cemetery, New Jersey, USA.