Born at Stowe, Grenville, the elder brother of Sir Richard Grenville (June 26^th), served as County  Member of Parliament for Cornwall in 1621 but became MP for Launceston in 1625. He was in this position when King Charles I decided to rule without Parliament in 1629. Despite, in Parliament, supporting Sir John Eliot of Port Eliot, a lifelong friend, he supported the Royalist cause in the Civil War.  A very popular man he was re-elected for Launceston in 1640 until he was removed in 1642 for supporting the King.

At the outbreak of the Civil War, Grenville declared for the King and quickly displayed his military skills at the Battles of Braddock Down and the The Battle of Stratton where the Parliamentarians were routed.   His bodyguard was the famous Anthony Payne (July 13^th) who was known as the Giant of Cornwall.

Grenville was killed at the Battle of Lansdowne (1643) as he led the Cornish infantry in attack.  His death was a devastating blow to the Royalist cause as he was the natural leader of their supporters and soldiers in the county.