He had previously served as the first Venetian Duke of Crete, and two terms as Podestà of Constantinople, twice as governor of Treviso, and three times as ambassador to the Holy See.

His dogate was marked by major domestic reforms, including the codification of civil law and the establishment of the Venetian Senate, but also against a mounting conflict with Emperor Frederick II, which broke into open war from 1237 to 1245.

[1][2] He remained in this post for two years, during which he acted almost as an autonomous agent, concluding peace and trade treaties on Venice's behalf with the Emperor of Nicaea, Theodore I Laskaris, in August 1219, and with the Sultan of Iconium, Kayqubad I, in March 1220.

[1][2] His understanding of his role is exemplified by his assumption of the Byzantine title of despot and the appropriation of the appellation "ruler of a quarter and a half of the Empire of Romania" that was normally attributed to the Doge.

[1] During the interregnum after the death of Latin Empress Yolanda in September 1219, he was among the most powerful magnates of the Empire along with regent Conon de Béthune.

[1] Tiepolo was back in Rome in April 1223, in order to obtain from Pope Honorius III the waiving of some ecclesiastical sanctions imposed on Venetian residents in the Latin Empire.

In foreign affairs, Tiepolo continued his predecessor's policy of safeguarding the overseas possessions secured after the Fourth Crusade, the defence of the Latin Empire of Constantinople, a division of spheres of influences with Venice's rivals, Genoa and Pisa, and a dense web of diplomatic and commercial treaties with both Italian and Mediterranean states.

Not only that, but Venice gradually moved to active opposition of Frederick, securing the appointment of Venetians as podestàs in Lombard cities, and encouraging them to resist the Emperor.

[1] After Frederick's victory over the League at the Battle of Cortenuova in 1237—in which Tiepolo's son, Pietro, led the Milanese forces and was taken prisoner—Venice allied with both Genoa and the Papacy.

An envisaged Papal invasion of the Kingdom of Sicily, from which Venice would have gained control of the ports of Barletta and Salpi, failed to materialize, but the Venetians proceeded to campaign in Emilia-Romagna, capturing Ferrara in 1240.

[1] Venetian agents also tried to oppose Frederick's policies in the Kingdom of Jerusalem, and in 1242, Tiepolo reconquered the rebellious city of Pula in Istria.

[1] This suspicion came at a time when a large part of the ruling establishment began growing weary of Tiepolo's policies and ambitions: indeed, in 1245, three leading Venetian patricians, Marino Morosini, Reniero Zeno and Giovanni da Canal, when captured and brought before Frederick II, repudiated the recently announced excommunication of the Emperor.