With the Army reduced in size after the Civil War, parts of the barracks fell out of military use. Part of the parade ground was purchased by the Irish Amateur Boxing Association in 1937 and made into what is now the National Stadium.
Other parts were leased out into private hands. In 1925 the barracks' married quarters were rented to Greenmount and Boyne Linen Company, which housed poor families there. In the 1950s, Dublin Corporation took over some of these buildings and used them for emergency housing for families from the inner city slums. The use of part of the barracks as social housing prompted a number of protests by the Dublin Housing Action Committee in the 1960s as a number of the buildings were in poor repair. Another part of the barracks was used by the Labour Court from 1947 until 1974. It was not until the 1970s that all of the remaining buildings returned to military use.
In the intervening years, the Irish Army's main challenge had been the Second World War or 'The Emergency', in which it was expanded to deal with possible threats to Irish neutrality. A new regiment was raised and based in Griffith Barracks. However, in the absence of foreign invasion the regiment's most challenging work proved to be a search and rescue operation in Dolphin's Barn for the victims of a German air raid in January 1941, which injured 22 people and caused a great deal of destruction. Most new recruits were demobilised at the war's end and the barracks was occupied by just one battalion.
In the 1970s, the Army was again expanded against the background of the Northern Ireland conflict and Griffith Barracks was again fully garrisoned by the 20th Battalion and the Motor Corps along with the reserve force, the FCA. By the 1990s, however, it was clear that Ireland did not need to maintain all the barracks that had been established by the British administration.