Harrison was born in
Hull on 12 November 1890. His father was a plater and boilermaker in the Earles Shipyard. After leaving school, Harrison studied at St John's College, York (now
York St John University) where he was Rugby club captain and also represented the College at cricket and swimming before becoming a teacher later at Lime Street School in Hull. In York, he caught the attention of the
York rugby league club, and played for them five times in 1911–12, scoring three tries. He returned to Hull in September 1912 and married Lillian on 1 September 1914. He was invited to join
Hull F.C. which included
Billy Batten, and played his first match on 5 September 1912. In 1913–14 season, he scored a record 52 tries and he went on to score a total of 106 tries in 116 matches for Hull up to 1916. Jack Harrison played on the and scored a
try in Hull F.C.'s 6–0 victory over
Wakefield Trinity in the
1914 Challenge Cup Final during the
1913–14 season at
Thrum Hall,
Halifax, in front of a crowd of 19,000. ==First World War==