He made the Football League referees list in 1954 at the age of thirty, and went on to have a seventeen-year career at this level.
His greatest domestic honour came when he took charge of the 1968 FA Cup Final between West Bromwich Albion and Everton at Wembley.
On 11 June 1967 he took charge of Sweden versus Bulgaria in the Råsunda Stadium, Solna, in that competition.
[4] As regards club competitions, Callaghan was in charge of, for example, Atlético Madrid against FK Vojvodina in their second round second leg tie in the European Cup on 14 December 1966 at the Estadio del Manzanares, when the two-leg scores tied at 3–3, and the result had to be decided by a tie-break match a week later.
Whilst refereeing a Football League Second Division match between Millwall and Sheffield United, the city of London was engulfed by "[t]orrential rain", causing the "abandonment of [the] game after 25 minutes by ... Callaghan ...".