[1] Widowed, Gritti moved to the Ottoman capital, Constantinople, where he engaged in trade, particularly of cereals, often in partnership with the Genoese merchant Pantaleo Coresi.

[1] Lacking an official appointment, however, his position was precarious, especially as, with another Ottoman–Venetian conflict looming in 1499, he used his commercial correspondence, sent via Corfu and the Ragusan merchant Nicolò Gondola, to transmit encoded information to the Venetian Senate regarding the movements of the Ottoman navy (referred to as "carpets" in one letter) and troop concentrations.

[1][2] This activity did not remain hidden from the Turks for long, however: after capturing couriers bearing Gritti's letters, in August 1499 he was imprisoned in the Yedikule Fortress, escaping execution only through his friendship with the grand vizier.

[1] Gritti nevertheless spent 32 months in the fortress, along with other Venetian merchants, coming close to death due to the privations of this long imprisonment.

Gritti's experience with the diplomatic customs of the Ottomans led to his being charged with overseeing the final formulation of the treaty's clauses, so as to remove any ambiguities and causes for misinterpretation.

[1] The war and his long imprisonment put an end to Gritti's commercial career, costing him the enormous sum of 24,000 ducats.

[1] In 1508, as the Republic's relations with the Holy Roman Empire broke down, leading to the outbreak of the War of the League of Cambrai, Gritti was appointed provveditore generale along with Giorgio Corner.

[1] Gritti was soon appointed as provveditore generale to the Venetian field army, where he distinguished himself for his energy and capacity to endure hardship.

[1] He participated in the disastrous Venetian defeat at the Battle of Agnadello against the French on 14 May, but managed to escape to Brescia,[4] carrying along a Banner of Saint Mark, that he later dedicated to the Santi Giovanni e Paolo church.

[9] Gritti instituted a harsh suppression of anti-Venetian elements in Padua, with arrests, executions, confiscations of property, and the exile of over 300 people to Venice.

His own capture of Padua was assisted by armed peasants, and on 23 July he urged the Signoria of Venice to embrace this movement as part of a broader strategy to turn the tide of the war.

[citation needed] Elected Doge in 1523, Gritti concluded a treaty with Charles V, ending Venice's active involvement in the Italian Wars.

He attempted to maintain the neutrality of the Republic in the face of the continued struggle between Charles and Francis, urging both to turn their attention to the advances of the Ottoman Empire in Hungary.