He served in high military posts during the Morean War against the Ottoman Empire, leading the Venetian conquest of Castelnuovo and Knin in Dalmatia, the capture of Monemvasia in Greece and of Valona and Kanina in Albania.
[1] Girolamo followed a conventional political career, being elected twice as a member of the Savi agli Ordini (in 1657 and 1659), a post typically earmarked for young nobles to gain experience in public affairs.
[1] In 1666, Girolamo was elected for the first time to the Venetian Senate, and went on to hold some of the highest offices in the Republic, as member of the Council of Ten in 1668–1669 and again in 1670–1671 and of the Savi di Terraferma in 1669.
[1] After his return to Venice, he was elected ducal councillor in 1677, to a second term at the Council of Ten in 1678, while also serving as state inquisitor and Provveditore sopra i Beni Inculti.
[1] In 1679, he was sent to a two-year stint as governor-general of Venetian Dalmatia (Provveditore Generale di Dalmazia), during which he busied himself with trying to address the declining population and the endemic economic and social problems of the province.
[1] After the end of his tenure in Dalmatia, in June 1682 Girolamo moved to the pinnacle of the Venetian overseas administration, as Provveditore Generale da Mar.
[2] Girolamo tried to preempt Morosini and seize the fortress of Santa Maura (Lefkada), which he believed to be lightly defended, before the arrival of the fleet from Venice.
[1] Within three years, Girolamo not only secured Venetian Dalmatia, but added to it a profitable territory 70 miles wide and 300 long; for his success, he was named Procurator of Saint Mark.
[5][7] This success allowed the Venetians to expand the area under their control along the coasts and interior of Epirus to Argyrokastron, Himara, Souli, and even the vicinity of Arta,[5] but an attempt to capture the port of Durazzo further north had to be aborted due to adverse weather.