Barthorp attended Wellington College until the end of the Second World War.
In September 1945, he joined the Rifle Brigade under universal conscription and was demobilised in 1958.
After some time with the Royal Hampshire Territorials, he exchanged for a regular commission in the Northamptonshire Regiment in which his family had served for three generations.
He was a member of the Victorian Military Society and contributed to their magazine Soldiers of the Queen.
Predeceased by his wife Penelope, they were survived by two sons and a daughter, grandchildren, and great-grandchildren.