He played in goal for Belfast Celtic, Linfield, and Dartford, was capped once by his country, and briefly managed Port Vale.
Diffin became a Port Vale director in 1944 and appointed team manager in October of that year.
[1] Diffin remained the effective manager until August 1945, when Billy Frith was appointed.
Diffin then concentrated on his board duties before being elected vice-chairman in 1946, finally stepping down in December 1957.
[2] Diffin ran a general drapery and boot merchants business in Belfast and established a road haulage company in England.