His education was at Saint Aloysius College and then at the University of Malta. He graduated as a doctor on 1990. His after specialisation was as a psychiatrist at Yale University (United States of America) Foreign a number of years he worked as a consultant within the Department of Health.
He is also a lecturer at the University of Malta.
He has authored numerous papers related to psychiatry. He represented the Nationalist Party in the Medical Board for the Maltese Electoral Commission. He contested the 2008 elections in the interest of the Nationalist Party getting elected to the House of Representatives of Malta.
Prime Minister Lawrence Gonzi appointed his as Parliamentary Secretary of Health in the Ministry of Social Policy, assisting Minister John Dalli.
Following Dalli"s resignation from the post of Minister for Social Policy, the portfolios of Health, Elderly and Community Care were assigned a Ministry. Cassar became the Minister for Health, Elderly and Community Care on 9 February 2010.
Mario Galea, retained his own position as Parliamentary Secretary for the Elderly and Community Care. After serving as a PN Member of Parliament since March 2013 and spokesperson for Culture, Doctor Cassar resigned after reports surfaced in the media of alleged gifts he accepted when he was still a Minister.
The gifts were said to have been given by a well known businessman who was the subject of various controversies, and included a car, CCTV cameras, and construction works on his house.
He was a Nationalist Member of Parliament until he resigned on November 1 2015, both from the Nationalist Party and Parliament. During his professional career, Cassar was President of the Malta Medical Students Association, an executive member within the Medical Association of Malta, the President of Yale Psychiatry Residents Association and an active member of the International Catholic Movement.
