Dr O’Callaghan graduated from the University of Melbourne in 1984 with a Bachelor of Dental Science degree. He then practiced as a general dentist in Melbourne for several years with a keen interest in orthodontic care. During this period, he attended as much continuing education in orthodontics as possible.
Following a period of study in the United States of America in 1990, Dr O’Callaghan applied for and was accepted to study for his specialist degree in orthodontics in Cleveland, Ohio, USA at Case Western Reserve University. Dr. O’Callaghan returned from the USA in 1993 and began practice in Box Hill and Ringwood localities.