From birth he was destined for a career in the Church, and in 1622 he was made Abbot Commendatory in the Abbey of SS. Leonardo and Apollonius of Canossa. However, he renounced to his religious habit three years later in order to follow a military career. He moved to the Holy Roman Empire, where he attended a military academy and joined the Imperial Army. In 1632, Borso was put in charge of an infantry regiment in the Battle of Lützen. In 1634, he fought in the Battle of Nördlingen. In 1640, he was summoned back to the Este territories by his nephew Francesco I, Duke of Modena to fight against Spanish troops from the Duchy of Milan. In 1641, he bought the Ducal Palace of Rivalta and during the next three years the palace was renovated and enlarged.