Pompeo Gabrielli was born in Rome on 22 August 1780. After completing his studies at the "Collegio Tolomei" in Siena, in 1801 he joined the newly constituted Noble Guard, and in 1805 was assigned to a cavalry regiment. In February 1808 he resisted the French occupation of Rome and was therefore arrested by decree of General Miollis. He soon became supportive of the Napoleonic regime, however, and shortly after was offered to join the Imperial Guard as a cavalry officer. He thus participated in the Napoleonic wars and fought in Austria (Battle of Wagram), Russia (where he was presented with the "Légion d'Honneur" by the emperor), Germany (where he was wounded during the battle of Leipzig), and finally at Waterloo.