Supem has been a member of the Sri Lanka Bar since 1987 where he practiced international human rights and immigration law. He successfully passed the Solicitors Final Exam of England and Wales in 1991 and became licensed to practice as a Solicitor in England and Wales . He obtained his Master of Law degree from the University of Maryland in 2019. He interned at an immigration firm called Julia M Toro Law Firm and later Clerked at the Office of Administrative Judge Hearings and completed a course and training to become a ‘Certified Mediator’ of
the State of Maryland.