Gribbin commenced his working life as a clerk at the Magistrates Court at Warwick in 1964. He later worked as a registrar in over nine court registries including Springsure, Herberton, Cairns, Beenleigh, Inala and Rockhampton. After being admitted as a legal practitioner in late 1984, he undertook a series of appointments as Acting Magistrate at Herberton, Cairns, Beenleigh, Inala and Rockhampton over a two-year period before being appointed as a Queensland Magistrate.[2]
In 1998, Queensland Courts established a Rules Committee to introduce and monitor the Uniform Civil Procedure Rules. Magistrate Gribbin served as one of the court's two representatives on the committee since its inception — a role he relinquished just prior to his retirement.[2]