John qualified in dentistry from the University of Wales in 2001, completing their vocational training in 2002 and general professional training in 2003. The following year, they were awarded Membership of the Faculty of Dental Surgery of the Royal College of Surgeons in Ireland. John completed three years' full-time orthodontic training in Birmingham in 2010 and was subsequently awarded Membership in Orthodontics from the Royal College of Surgeons in Edinburgh. They were an honorary clinical lecturer at the University of Birmingham for four years and spent a year as a lecturer in restorative dentistry at Cork University. They completed a Master of Philosophy in Orthodontics from the University of Birmingham in 2012 and was awarded John's Fellowship from the Royal College of Surgeons in Edinburgh in 2016.

John has held a number of posts at senior house officer level in oral and maxillofacial surgery, restorative dentistry, community dentistry, paediatric dentistry, dental public health and oral surgery. They have presented at national and international conferences and have published numerous peer-reviewed articles in the scientific literature.