He served as a junior officer with the Pragmatic Army in the Dutch Republic and Germany during the War of the Austrian Succession.

[3] Whitwell was educated at Winchester College and commissioned as an ensign in the 3rd regiment of Foot Guards and lieutenant in the Army in 1739.

[10] Griffin was appointed Knight Companion of the Order of the Bath on 11 April 1761[11] and inherited Audley End House outright when his aunt died in 1762.

[14] During the political crisis in the early 1780s at the end of the American Revolutionary War he was generally a supporter of William Pitt the Younger.

[3] Griffin became colonel of the 4th Dragoons in March 1788, was additionally created 1st Baron Braybrooke on 30 August 1788[16] and was promoted to field marshal on 30 July 1796.