Cassar was born on April 27, 1958, in Malta, and graduated from Algonquin College in Ottawa, Ontario, Canada. During his adult life, he began a career of directing and producing episodes for several TV series and film-related works. His most notable contribution was to the TV series 24, being the producer of its first to seventh seasons. In 2006, Cassar won the Primetime Emmy Award for Outstanding Directing for a Drama Series for his work on "Day 5: 7:00 a.m. – 8:00 a.m.". He is also the co-founder of the Motion Picture Industry Charitable Alliance, which hosts an annual charity auction, "Lights, Camera, Auction".