Despite serious shortages in manpower and materials during the First World War, a rise in revenue due to increased passenger loads resulted in the tramway debt being paid off in 1917. Between 1922 and 1924 the system was expanded to over 270 miles with many route extensions and the acquisition of the independent tramways of Paisley and Airdrie along with the Glasgow Subway railway. A through service of trams between Airdrie and Paisley, over twenty miles, coinciding with a reduction in long-distance fares to a maximum of two pence, gave the Corporation a virtual monopoly of street transport in the Greater Glasgow area. This was aided by its developing bus services, especially after the 1930 Road Traffic Act forbade any other operator from carrying passengers purely within the city boundary.
From 1927 the fleet of tramcars, many of which dated from the early days of electric traction, were improved by having the upper deck open balconies enclosed and new trucks and motors fitted to provide higher speeds. Some of these survived for up to sixty years. A programme to build a fleet of luxury "bogie" cars, the "Coronations", began in 1937 to coincide with the coronation of George VI and the Empire Exhibition held at Bellahouston Park in 1938. When the Second World War halted further production in 1940, 150 cars had been built. Despite shortages of maintenance materials and the 1941 air raids, the tramways survived the war virtually intact and carried ever-increasing loads, particularly on routes serving the shipyards.
Following 1945 there were extensions to several routes, 150 modified "Coronation" cars (named "Cunarders") were built, and the Pinkston power station in Springburn which supplied electricity for the tramways was modernised, all serving to make the future of the system appear secure. However maintenance costs were rising and, as a result of the growth of new housing areas not served by the trams, alternative transport modes were being considered. Fare increases were inevitable and the days of cheap tram travel were over.