Cassidy held academic positions in Montreal, Ottawa, Toronto, Southampton, and Durham. He became an Anglican in 1993, was licensed as an Anglican priest in 1996, and was a member of the theology department and Principal of St Chad's College from 1997. Over an extended period of time (beginning in 1995), the college bursar, Christine Starkey, stole £488,000 from the college. Starkey was eventually found out during an internal audit: her house was sold and the CPS was able initially to recover approximately one third of the money that had been stolen. The rest of the money was later recovered.