Mythily graduated from the Lady Hardinge Medical College, India. She received her PhD in Gambling Studies from Monash University and is currently Director of the Research Division and Lead Investigator of the Programme of Mental Health Policy Studies at the Institute of Mental Health (IMH). She also has a concurrent teaching appointment at the Lee Kong Chian School of Medicine and Saw Swee Hock School of Public Health, National University Singapore. She is also a consultant with the Ministry of Health, Singapore.

She has worked in the field of mental health for more than 15 years. She was the Co-Principal Investigator of three nation-wide studies – the first and second Singapore Mental Health Study, surveys that established the prevalence of select mental disorders in the adult population of Singapore; and the Well-being of the Singapore Elderly study, a survey among older adults that aims to establish the prevalence, risk factors and cost associated with dementia in Singapore. She has over 300 publications in peer-reviewed journals and is a reviewer with many international journals.