In 1511 he was vice-podestà of Cologna Veneta, in 1515 an official at the Dogana da Mar - the maritime customs office- and in 1516, with a donation to the Republic of 200 ducats, he secured the office of provveditore and captain in Legnago, in the Verona countryside.
His task was to aid in the construction of the "fortezza nova" at Legnago, strongly desired by doge Andrea Gritti, a project under the direction of the commander-in-chief of the Venetian land forces Francesco Maria I della Rovere.
On 15 December 1530 the chief architect working on the project, the Ferrarese Sigismondo de Fantis was fired for incompetency, to be replaced by his aide, the Veronese Michele Sanmicheli, whose Porta di San Martino had gained considerable acclaim as a tasteful yet function example of military engineering.
In 1533 he was nominated savio alle acque, then procurator in the zonta dei nove- an additional group of councillors that sat with the Council of Ten- then in 1539, together with the duke of Urbino, inspector of the fortresses of the Venetian mainland, and then, on 27 December 1539, with Vincenzo Grimani, special ambassador to the courts of Francis I in France and emperor Charles V in Flanders, with the objective of convincing the two rival monarchs to set aside their differences and join Venice in an anti-Ottoman coalition.
In the following years, Antonio Cappello was appointed to more prestigious public offices: he sat in the consiglio alle acque, then in the committee that superintended the fortifications of Zadar, then he was provveditor over the Republic's fortifications, In 1543 finally he was dispatched to negotiate the purchase of the fortress of Marano Lagunare in eastern Friuli, seized the previous year by a band of rogue Venetian subjects loyal to Florentine renegade adventurer Piero Strozzi from the Austrians, and which threatened to draw the Republic into the Italian War of 1542-46 then raging between Habsburgs and Valois.
The affair was concluded with the hefty disbursement in favour of Piero Strozzi of 35,000 ducats, in exchange of which the Venetians gained the small but strategic town.