John Hornby was born in the Newcastle upon Tyne suburb of Elswick, the son of a Railways Board of Trade Inspector. The family moved to London and John became a well-known referee, mostly in the London area until after World War I. He officiated at many matches in the Athenian, Isthmian, and London Leagues, as well as in the London Combination and FA Cup and Amateur Cup matches. He was one of the linesmen for the third-place play-off match between Netherlands and Sweden at the 1908 Olympics. He kept refereeing until the 1920s, and in 1922 took charge of a friendly between Chelsea and Fulham at Stamford Bridge. Hornby was a railway clerk, and the one-time president of the London Society of Association Referees, and was also the organiser of the Southern District of the Referee’s Union. His brother Lawrence was also a referee.