[8][11] He transferred to the Regular Army as a lieutenant in the Somerset Light Infantry on 22 March 1917 and was assigned to the Middle Eastern theatre of operations.

[16] Harding's many fellow students there included Gerald Templer, Gerard Bucknall, Gordon MacMillan, Alexander Galloway, Philip Gregson-Ellis and Richard McCreery while the instructors included men such as Bernard Paget, Richard O'Connor and Bernard Montgomery, the last of whom was destined to make a significant contribution towards Harding's later military career.

[22][21] When Lieutenant Generals Richard O'Connor and Philip Neame were captured in April 1941, Harding took temporary command of the WDF, in which capacity he took the decision to hold Tobruk.

[23] He was promoted to the substantive rank of colonel on 9 August 1941 (with seniority backdated to 1 January 1941)[24] and was later awarded the Distinguished Service Order (DSO).

[27] He was promoted to acting major-general on 26 January 1942[28] and became Deputy Director of Military Training Middle East Command,[23] in which capacity he was again mentioned in despatches in the summer of 1942.

[30] He led his forward headquarters from a tank and then a jeep and, during the pursuit of the Axis forces to Tripoli, was subsequently wounded by shell splinters in January 1943.

[20] He was appointed a Knight Commander of the Order of the Bath on 16 June 1944 for his service in Italy,[35] and promoted to the substantive rank of major general on 13 July 1944.

[38] Promoted after the war to lieutenant general on 19 August 1946,[39] Harding succeeded Alexander as commander of British forces in the Mediterranean in November 1946.

[54] Harding took strict measures to improve the security situation in Cyprus, EOKA having declared an armed struggle against the British on 1 April 1955.

[55] To this end, Harding instituted a number of unprecedented measures including curfews, school closures, the establishment of internment camps, the indefinite detention of suspects without trial and the imposition of capital punishment for offences such as carrying weapons, incendiary devices or any material that could be used in a bomb.

[60] Facing growing criticism in the United Kingdom about the methods he used and their lack of effectiveness, Harding resigned as Governor of Cyprus on 22 October 1957 and was replaced by Sir Hugh Foot.