Kassis has represented Lebanon in a number of Chess Olympiads, including:
- 1994, where he scored 3½/9 on board four.[2]
- 1996, scoring 4½/9 on first reserve.[3]
- 1998, scoring 6½/11 on first reserve.[4]
- 2002, scoring 5/10 on first reserve.[5]
- 2004, scoring 4/9 on board four.[6]
- 2006, scoring 5/9 on board three.[7]
- 2008, scoring 5½/9 on board three[8]
- 2010, scoring 4/10 on board four.[9]
- 2012, scoring 6/10 on board four.[10]
- 2014, scoring 5½/9 on board two[11]
- 2016, scoring 3/9 on board three.[12]
- 2018, scoring 3½/8 on board four.[13]
He won the Lebanese Chess Championship in 1995, 2018 and 2019.[14]
He qualified to play in the Chess World Cup 2021, where he was defeated 2-0 by Yuri Kuzubov in the first round.[15]