In 1763 the last Este Duke of Modena Ercole III (who did not die until 1803) signed a treaty with the Empress Maria Theresa engaging the nine-year old Ferdinand to his only daughter Maria Beatrice, making him thus his heir. There had been an earlier treaty in 1753 making Ferdinand's older brother Peter Leopold the heir to the Duchy of Modena, but in 1761 Peter Leopold became heir to the Grand Duchy of Tuscany which required a change to the Modena agreement.
In 1771 the Imperial Reichstag approved the eventual investiture of Ferdinand with the imperial fiefs held by Ercole III.
Marriage and family
Ferdinand and his wife Maria Beatrice of Modena
On 15 October 1771 Ferdinand in effect married Maria Beatrice Ricciarda d'Este (7 April 1750-14 Nov 1829), only surviving child of Duke Ercole III of Modena and Reggio (although the marriage was not a requirement of Ferdinand's eventual succession). Johann Adolph Hasse composed his opera Il Ruggiero for this occasion.
Ferdinand and Maria Beatrice Ricciarda had nine children:
Ferdinand became Governor of the Duchy of Milan on his marriage in 1771, as long as his father-in-law Ercole III d'Este still ruled the Duchy of Modena. He and his family lived in Milan.
In 1780 Ferdinand was confirmed Governor of Lombardy by his brother the new Holy Roman Emperor Joseph II. In 1796 Napoleon's invasion of Milan forced the family to flee the French forces. Duke Ercole III also had to flee Modena which overthrew the monarchy and joined the Cisalpine Republic.
By the Treaty of Campo Formio in 1797 Duke Ercole III was granted the Duchy of Breisgau, a Habsburg territory in southwest Germany. When Ercole III died in 1803, Ferdinand succeeded as Duke of Breisgau, as well as Titular Duke of Modena and Reggio. By the Treaty of Pressburg in 1805 Ferdinand ceded the Duchy of Breisgau to the Grand Duchy of Baden. Ferdinand died the following year in Vienna.
In 1814 Ferdinand's eldest surviving son Francis IV was recognised as Duke of Modena by the Congress of Vienna.