Sebastian has conducted over 100 missions to Africa, the Middle East, and Asia, with a particular focus on conflict and post-conflict settings, conducting evaluation, diplomatic, and representative duties. Sebastian holds BA and MA degrees from Trinity College Dublin, an MPH degree from the University of Cape Town, is an adjunct assistant professor at Trinity College Dublin and an academic affiliate of the Center for AIDS Prevention Studies at the University of California, San Francisco. Sebastian was a Dalan external Consultant for the 2017 external evaluation of the President’s Post Ebola Recovery Priorities’ commissioned by the Office of the Chief of Staff, State House, Sierra Leone.