Before the 1954 World Cup, he went to Sampdoria and then concluded playing in Serie A with Padova.

Giacomo Mari is one of five Italian players (the others are Giampiero Boniperti, Gino Cappello, Ermes Muccinelli and Egisto Pandolfini) that played for Italy in both the 1950 and 1954 World Cups.

With the Italy national team, he debuted at the 1948 London Olympics, against Paraguay;[1] he also featured against Switzerland at the 1954 World Cup.

A tireless runner, Giacomo Mari was a classic halfback, waiting in the folds of midfield ready to halt the attack of the opposing forwards and wings.

This biographical article related to association football in Italy, about a midfielder born in the 1920s, is a stub.