Born in Blackpool,[2] he started his career playing for Bolton Wanderers Youth and Reserve sides from the 2005–06 to the 2007–08 season and was named Academy Player of the Year in 2007.He also played for the Liverpool Dream Team of the late 90s [3] In the summer of 2007 he made his first team debut for Bolton in a defeat to Hibernian.
[4] After leaving Bolton in the summer of 2008, he was offered contracts at a number of English clubs including Doncaster Rovers and Luton Town, but Cassidy turned down these offers to accept a contract at Cypriot First Division club Enosis Neon Paralimni.
[5][6] He made his debut for the Cypriot club on 29 August 2009, in his side's 3–0 defeat to Apollon Limassol, coming on as a second-half substitute.
[8] After one year with Enosi Neon Paralimniou he left the club having made a total of 17 appearances scoring no goals.
[9] After leaving Enosis, Cassidy moved to one of the biggest clubs of the island of Cyprus, AEL Limassol.