Del Bello and his younger brother Rolando were introduced to the game at a young age, as their father worked at a tennis club.

Marcello made his Grand Slam debut at Wimbledon in 1947, losing in round one to Enrique Morea.

[3] At Roland Garros (held after Wimbledon for the last time), Del Bello lost in round three to Philippe Washer.

[4] At Roland Garros in 1948, Del Bello reached the quarter finals, where he lost to Budge Patty.

By 1951 Del Bello's career was beginning to decline and he lost in round one of the French to South African Syd Levy in straight sets, and Wimbledon.