 Callinan became a member of An Garda Síochána in 1973 and was promoted to the position of sergeant in 1986.Callinan quickly rose through the ranks of the organisation; he mainly served in Dublin, but he also spent had spells stationed in Waterford and Mayo.As member of the Central Detective Unit, Callinan began to be assigned to high profile cases and began to become a prominent official within the force.