A highly cultured man who spoke several languages, Giustinian served as the Most Serene Republic's Ambassador to the Kingdom of France.

This strategy led to Giustinian's reign being a time of military victories for the Republic, which were exciting for Venetians who had spent decades watching their empire decline, suffering military defeats, engaging in prolonged sieges, and generally being forced to agree to onerous terms in peace treaties.

In 1686 and 1687, Morosini secured several dramatic victories over the Ottoman Empire, conquering Preveza, Kalamata, Navarino and the island of Santa Maura.

In his four-and-a-half-year reign, all major decisions were left to his advisers, a fact which led some Venetians to criticize him.

Later, a humorous poem circulated about the two attending physicians, Ton and Dolfin (whose names translate as tuna and dolphin), claiming that the doge had been killed by two fish.