Brudenell was the third son of the 3rd Earl of Cardigan and Elizabeth Bruce and a younger brother of the 1st Duke of Montagu and 4th Earl of Cardigan and the 5th Earl of Cardigan. He was educated at Winchester College and Oriel College, Oxford; on 27 January 1759, he married Anne Bishopp, a daughter of Sir Cecil Bishopp, 6th Baronet.
Brudenell was commissioned as Ensign in the First Foot Guards in 1748, promoted to Captain in 1751, Lieutenant-Colonel in 1758 and Colonel in 1762. In 1763 he became colonel of the 16th Regiment of Foot, a post he held until his removal to the 4th Regiment of Foot in 1765. He was also Lieutenant-Governor of Windsor Castle from 1752, and Vice-Chamberlain to Queen Charlotte from 1766 until his death.
He served as MP for Great Bedwyn from 1756–61 and for Marlborough from 1761-68. However, he took little interest in politics, generally supporting each successive administration so as to avoid any risk to his military advancement.
As he predeceased his childless elder brothers, Brudenell's son, Robert became the 6th Earl of Cardigan.
- Lewis Namier & John Brooke, The History of Parliament: The House of Commons 1754-1790 (London: HMSO, 1964)
- Leigh Rayment's Peerage Pages [self-published source][better source needed]
|Parliament of Great Britain|
Sir Robert Hildyard
| Member of Parliament for Great Bedwyn
With: Sir Robert Hildyard
Hon. John Ward
Sir John Cotton
| Member of Parliament for Marlborough
With: Lord Brudenell 1761–1762
Sir James Tylney-Long 1762–1768
Sir James Tylney-Long
| Vice Chamberlain to Queen Charlotte
Hon. Charles FitzRoy
| Colonel of the 4th (The King's Own) Regiment of Foot