[2] Entering the British army in 1797 as an Ensign in the 32rd Regiment of Foot[3] Bentinck then purchased promotion to Lieutenant and subsequently Captain in the 24th Light Dragoons.
[4][5] 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).
[4] Cavendish-Bentinck was approached by his cousin, Thomas Thynne, 2nd Marquess of Bath about becoming a member of parliament (MP) after the conclusion of the Napoleonic Wars.
[12][13] In 1824 Cavendish-Bentinck vacated his seat at Weobley at the request of the Marquess of Bath and was invited by the Duke of Wellington to become MP for Queenborough on the Isle of Sheppey in Kent.
[2][14] Despite its status as a rotten borough and being much controlled by the Board of Ordnance Queenborough did have independently minded voters and at the 1826 general election Cavendish-Bentinck was voted out of office.