He received his episcopal consecration on 19 December from Cardinal Francesco Saverio de Zelada.

In 1786 he was appointed Apostolic Nuncio in Brussels or perhaps more precisely the ecclesiastical superior of the Mission sui iuris of Batavia, with responsibility for the Austrian Netherlands.

He was expelled on the orders of Emperor Joseph II the following year, as he was suspected of supporting the Brabant Revolution.

He received Pope Pius VI in Siena when he fled from Rome, expelled by the pro-French revolutionaries.

Zondadari was among the few of his peers (14 in all) admitted by Napoleon to his wedding ceremony with Marie Louise of Austria in the Louvre on 2 April 1810.