Prior to coming to the Bar, Thomas was a prosecutor for the NSW Police Force for more than 10 years, appearing in a range of criminal prosecutions, road transport legislation proceedings, Apprehended Violence Order (AVO) proceedings as well as interlocutory and civil procedure applications.

Upon being promoted to the rank of Sergeant, Thomas became a member of the Prosecutor Training Unit that was responsible for the training and assessment of police prosecutors. As part of this role, Thomas provided lectures in topics related to evidence, AVOs, criminal procedure, transport legislation and advocacy.

Before joining the NSW Police Force, Thomas worked for the Legal Directorate of the Department of Education and Training NSW.