He was MP for Marlborough in Wiltshire from 1818 to 1829, before inheriting the earldom from his father in 1837. By this time he was a serving army officer. In 1833, he had been forced to resign from the 15th Hussars because of conflicts with fellow officers, but in 1836 he took command of the 11th Hussars, using his own fortune to improve its performance. He was prosecuted in 1841 for a duel with one of his own officers, but was acquitted. His most famous exploit was when, in command of the light cavalry at the Battle of Balaclava, he led the so-called Charge of the Light Brigade. It was during his period in the Crimea that he "invented" the garment known as a cardigan in his memory.
{| border="2" align="center"
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|width="30%" align="center"|Preceded by:
Robert Brundell
|width="40%" align="center"|Earl of Cardigan
|width="30%" align="center" rowspan="2"|Followed by:
George Brundell
|}