He was killed in action in the Second World War during fighting in the Low Countries in September 1944 whilst leading a company of the Coldstream Guards.

[1] He was a member of the Conservative Party, and was selected as the official candidate of the Wartime Coalition for the West Derbyshire by-election on 18 February 1944, in the constituency local to Chatsworth.

He was faced by Charles Frederick White, Jr., who resigned from the Labour Party to run as an Independent candidate, evading the Wartime Coalition's ban on partisan campaigning.

Of the townsfolk and villagers who turned out and cheered the Allies and, in some cases, decorated their tanks, Hartington wrote to his wife of feeling "so unworthy of it all living as I have in reasonable safety and comfort during these years.....

"[3] On 9 September 1944, Hartington was shot dead at the age of 26 by a sniper whilst leading a company trying to capture the town of Heppen in Belgium from troops of the German Waffen-SS.