Started working life as a physiotherapist working before completing a BSc (Honours) at the University of Western Ontario Canada in 1986. In 1988 returned to New Zealand to attend medical school at Otago (MBChB 1992).
Following medical school she completed physician training and neurology in Auckland, New Zealand. One year of neurology training was spent as the travelling Australasian clinical fellow at the Royal Free Hospital in London, England followed by a two year fellowship in multiple sclerosis at the London Health Sciences University Hospital in London Ontario. In 2003 Dr Mason returned to New Zealand to take up a full time specialist neurology position at Christchurch Hospital.
In addition to her hospital position she is also a clinical senior lecturer at the Christchurch campus of the University of Otago medical school and is affiliated with the New Zealand Brain Research Institute. Her principal research interest is in inflammatory brain diseases and multiple sclerosis and she is Medical director of Multiple Sclerosis New Zealand (MSNZ). She was one of the lead investigators of the New Zealand Multiple Sclerosis Prevalence study and has been involved in a number of gene studies in MS. She is currently the principal investigator for the New Zealand Multiple Sclerosis Incidence study and the lead investigator for the Vitamin D intervention trial in MS.