[1] Casella started playing hockey at age six in Argentina for San Fernando.

[8] In 2014, Casella made his debut for Argentina, representing the Under 18 national team at a qualifier for the 2014 Summer Youth Olympics.

At the tournament he scored 18 goals, helping Argentina to a gold medal and qualification to the Junior World Cup.

[9] Casella again represented Argentina at the Junior World Cup in Lucknow, India, where the team finished 5th.

[10] Casella debuted for the senior national team in 2015, in a test series against the United States, in Boston.