John was born in Wickham near Portsmouth, the younger son of George William Carpenter-Garnier and his wife, Cheston Isolda Prideaux-Brune.  [His father was a brother of John Trefusis Carpenter-Garnier whose name is on the 1914-18 Memorial.]

He was educated at Radley and Matriculated in 1940. He joined the Scots Guards and trained at Sandhurst. He was posted missing, initially, but died on 22 September 1943.

He is buried in the Salerno Cemetery. Plot V. A. 20.

He is commemorated on the War Memorial at Wickham, Hampshire, as is his uncle, and in the Royal Memorial Chapel, Sandhurst.