Originally from Bristol, Casson joined Gloucester's Academy whilst studying at Hartpury College, making one senior appearance for Gloucester before going to University.
After graduating he joined Warriors and has spent time on loan at Coventry and Cinderford.
The second-row said: "I am very much looking forward to joining up with Leeds Carnegie. It is a very competitive squad and I am hungry to get out there and play some rugby.
"The Greene King IPA Championship is a very competitive league and I am looking forward to testing myself in that environment.
"Obviously it helps that Jon Clarke has also just made the move up from Worcester. I would have been happy to come up on my own but having an experienced player to turn to who I already know, will hopefully mean I can settle in easier."
Casson has played for England Academies Under 19s, England Students and captained the England Counties Under 20s side earlier in his career.