[citation needed] Belonging to the branch of the parish of S. Moisè, he was the son of Giberto who had defeated the Genoese in the battle near Settepozzi, and of Maria of Gratone Dandolo of S. Polo.
According to all the oldest genealogies, his grandfather was called Giacomo: it is, therefore, to be considered a mistake of the most recent literature the attribution to him of the vicedoge Raniero as an ancestor and then of the Doge Enrico as great-grandfather.
The news of his election to doge reached him while he was fighting in military action against Istria and Trieste, which expanded into an open war in the following year, also involving Venice's perennial enemy, the Patriarchate of Aquileia and the Papal States.
After Dandolo signed the peace Treaty of Ravenna with Ancona, a new military theatre opened through the revolt in Crete led by the Greek noble Alexios Kallergis and backed by the Byzantine emperor Michael VIII, Venice's rival for the domination of the eastern Mediterranean.
These conflicts forced the Republic of Venice to negotiate peace agreements with Charles of Anjou and Philip III of France, concluding an alliance with the former in the Treaty of Orvieto.