In 2000 he played Cracker Bob in Highlander: Endgame and in 2001 he had a starring role in the drama series The Beast, which was cancelled after five episodes. Cassidy first came to fame as the host of Australian television show Kids Company, on Channel 10. He also appeared in many Shakespeare productions across Australia.
Cassidy's career took off when he played Cracker Bob in Highlander: Endgame in 2000 and starred in the short-lived drama series The Beast in 2001. His breakthrough came as the host of Kids Company on Channel 10, a role that launched his fame in Australia. He also showcased his acting skills in various Shakespearean productions.