[1] Callaghan was born in Dublin and began his career with English club Stoke City progressing through the youth ranks at the Victoria Ground and signed a professional contract in 1984.
On 26 February 1985, he produced a great performance as Ireland beat England 1–0 in the opening qualifying match of the 1986 UEFA European Under-18 Championship.
He was selected for the 1985 FIFA World Youth Championship finals in the Soviet Union but on 19 August, five days before it was scheduled to start, he was recalled by Stoke City as he was needed for first team duty by manager Mick Mills the following Saturday.
The defender made two Republic of Ireland national under-21 football team appearances, playing alongside Denis Irwin and Pat Dolan in a 0–0 draw in Belgium in September 1986 and in the 2–1 defeat to Scotland at Oriel Park in October 1987.
He is currently a coach education tutor for the Football Association of Ireland and sports development officer for Dublin City Council.
[4] Despite financial constraints at the club, he led his team to a comfortable midtable finish in a season that included a 4–0 victory over Shamrock Rovers and Bohs' first league win in Tallaght Stadium.
He was rewarded for this good season by being offered a two-year contract extension by the Bohs board of directors, which he signed in November 2012.