Entering the British army in 1797 as an Ensign in the 32rd Regiment of Foot Bentinck then purchased promotion to Lieutenant and subsequently Captain in the 24th Light Dragoons. Placed on half-pay Bentinck was attached to the combined Russian and Austrian army in Italy during the War of the Second Coalition during which period he participated in the battles of Novi (1799) and Marengo (1800) as well as being present at the Siege of Alexandria (1801).