After the war, Martin remained in the army, attended the Staff College, Quetta from 1926 to 1927, and became a prominent golfer. As a member of the Royal Portrush Golf Club, he won the Irish Amateur Open Championship in 1920 and 1923, and the Army golf championship in 1928. He stood in for Cyril Tolley to play in the 1928 Walker Cup as part of the British and Irish team, where he was partnered with another Portrush golfer, Major Charles Hezlet. The British and Irish team had their worst showing ever that year, losing eleven matches to one. Hezlet had been the first Irishman on a Walker Cup team, in 1924, and Martin was the second. Martin also played several international matches for Ireland, captaining the team in 1930. He later became chairman of the Royal Portrush, and headed the club at the time it hosted the 1951 Open Championship, to date the only time the championship has been held outside Great Britain. He presented the winner's trophy to Max Faulkner.
During the early stages of the Second World War Martin commanded the 18th Field Regiment, Royal Artillery, leading the regiment overseas to France in September 1939. The regiment formed part of the 2nd Infantry Division, then commanded by Major GeneralHenry Loyd, which itself formed part of the British Expeditionary Force and, not immediately engaged in combat, the regiment spent most of the "Phoney War" digging defensive positions. In February 1940 the regiment transferred from the 2nd Division to the 48th Infantry Division, a first-line Territorial Army formation commanded by Major General Andrew Thorne, which had recently arrived in France the month before. The policy within the BEF was for the Regular Army formations to transfer units to the TA units which, for various reasons, were not as well trained as their Regular counterparts, and this would, in theory, strengthen the Territorial formations. Sometime after this, Martin was appointed as Commander, Royal Artillery in the 50th Infantry Division, another TA formation which, in April 1941, moved from the United Kingdom to the Middle East. In March 1942 Martin was promoted to Brigadier Royal Artillery of the British Eighth Army, responsible for all of the army's artillery units. He pushed heavily for centralised control of artillery, reversing an earlier policy of dispersing the guns to support small forces. This approach bore fruit at the First Battle of El Alamein in July 1942, where concentrated artillery helped stall a German advance into Egypt. However, in August, Martin was sacked and sent home; the new Eighth Army commander, Lieutenant General Bernard Montgomery, blamed him for the previous policy of dispersion and wished to replace him with a new officer. Martin's successor was Brigadier Sidney Kirkman, one of Montgomery's protégés, later to command a corps in Italy and become a full general.
