Beyond all other interests, which included politics and the preservation of the ancient privileges of the aristocracy against the climate of the period, Brudenell committed himself to a career in the army. At the age of 22, as a captain in the Northamptonshire Yeomanry cavalry, he formed his own troop of horse, armed from official stocks, to guard against possible reformist demonstrations in Northamptonshire. On 6 May 1824, at the age of 27, he joined the 8th King's Royal Irish Hussars. Making extensive use of the purchase of commissions system then in use, he became a lieutenant in January 1825, a captain in June 1826, a major in August 1830 and a lieutenant-colonel, albeit on half-pay, only three months later, on 3 December 1830. He obtained command of the 15th The King's Hussars—at a reported premium of £35,000 ()—on 16 March 1832.