Leonardo's political ascent began at the age of nineteen, when he became a lawyer in the "Giudici di Petizion", a magistracy concerned mainly with financial scandals and bankruptcies, for which he had Filippo Loredan as guarantor. During his political career, he held multiple high positions such as chamberlain of the Comùn, wise man of the council, podestà of Padua, and Procurator of Saint Mark's.Barzman, Karen-edis (2017). The Limits of Identity: Early Modern Venice, Dalmatia, and the Representation of Difference. p. 124. On 31 March 1495, he was one of the three designated by Doge Agostino Barbarigo to negotiate the alliance between Venice, Pope Alexander VI, Holy Roman Emperor Maximilian I of Habsburg, the Spanish rulers Ferdinand V and Isabella I and the Duke of Milan Ludovico Maria Sforza (King Henry VII of England also joined), with the aim of countering the military operations of the King of France Charles VIII who had, almost without encountering military resistance, entered Naples in February. The army of the League, led by the Marquis of Mantua Francesco II Gonzaga, in the Battle of Fornovo on 6 July forced the French army to withdraw from Italian territory. In October of the same year, Loredan signed the agreement for the conduct of Niccolò Orsini, count of Pitigliano, to the services of the Republic of Venice as governor general of the land militias for the period of three to four years. In January 1497, Loredan, with the wise man of the Terraferma Lodovico Venier, ratified the surrender of Taranto on behalf of the Doge.
