Pre-1908, Parnell was a commissioned officer in the British Army's 2nd (South) Middlesex Volunteer Reserve Corps, a unit with a high reputation for rifle sports marksmanship in British Army military circles. Post-1908 he served with the 13th County of London Regiment ("The Kensingtons"), Territorial Force.[3]
In October 1917, his only child, Leslie Parnell, was killed during the Battle of Passchendaele as a subaltern with the 2nd Battalion of the 4th East Lancashire Regiment (on attachment from his father's corps) aged 20.[5]
Parnell was demobilised at the war's end in 1918 with the rank of Major.
Death
He died on 2 February 1941 in Totnes, in the county of Devon, at the age of 65. His grave is located at St. Mary's Church, Long Ditton, in the county of Surrey, England.
