Dr Geenty received his dental training at Otago University in New Zealand, graduating with a Bachelor of Dental Surgery (BDS) in 1975. He spent two years as Dental Registrar at a provincial hospital before returning to Otago to begin post-graduate training in orthodontics.
Dr Geenty started practice in Wollongong in 1981. In 1985 he was appointed part-time Clinical Associate in Orthodontics at Westmead Hospital and in 1993, a Senior Clinical Associate at the University of Sydney. In 2008 he was appointed Clinical Senior Lecturer at the University of Sydney.
Dr Geenty spends two days a month teaching post-graduate students at Sydney University. He has had several original articles published in scientific journals and he lectures to orthodontists and dentists in Australia and overseas.
Dr Geenty is a keen runner and competes in both 10km and half marathon events.