Born in Venice, Lorenzo Tiepolo was the son of Doge Jacopo Tiepolo. His first dogaressa was Agnese Ghisi. It is a matter of debate if his second wife, Marguerite, was either the daughter of the King of Romania or of Bohemund of Brienne, ruler of Rascia. Tiepolo also demonstrated skill as commander when, during the War of Saint Sabas with Genoa, he defeated the Genoese at Acre in 1257. He served also as a podestà of Fano.
In 1268, after the death of Reniero Zeno, Lorenzo was elected as Doge on July 23 of that year, with 25 votes out of 41. Although beloved by the population, he attracted the hostility of the Venetian nobility for his nepotism towards his sons. The position of Cancellier Grande ("Great Chancellor") was therefore created to thwart such a behaviour.
In 1270, an important treaty of peace was signed with Genoa at Cremona, confirming the Venetian predominance in the Adriatic Sea; however, in that same year a war broke out between Venice and a league of Italian cities including Bologna, Treviso, Verona, Mantua, Ferrara, Cremona, Recanati, and Ancona due to commercial disputes. After an initial setback in 1271, the Venetians were able to regain the upper hand and the terms of peace were favourable to Venice.
Under his dogado, in 1273, Marco Polo began his journey to China. He was to return only in 1295.
Tiepolo died in Venice in 1275 and was buried with his father in the Dominican church of San Zanipolo.