In 1953, after studying philosophy in Rome, Gallo was asked to leave Italy for missions, and he was sent to São Paulo, Brazil, where he attended theology courses.

[5][6][7] In 1960, Gallo was sent as a chaplain to the training ship Garaventa, trying to introduce a different setting in teaching and to replace the repressive methods with an education based upon trust and freedom.

Two months later, he was assigned as assistant pastor to the parish of Mount Carmel, where he remained until 1970, when Cardinal Siri moved back to Capraia.

Some time later, he was welcomed by the parish priest of St. Benedict at Port of Genoa, Don Federico Rebora, and together with a small group he established the Community of San Benedetto al Porto.

"[9] Since the foundation of the Community of San Benedetto al Porto, Gallo was committed to pacifism and to the recovery of marginalized people, even advocating for the legalization of soft drugs.