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 as well as interlocutory and civil procedure applications.

Thomas was part of the Prosecutor Training Unit and responsible for the training and assessment of police prosecutors. Thomas had given lectures in topics related to evidence, criminal procedure and advocacy.

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