Studying Moral Philosophy and Political Economy at the University of Glasgow, he failed to graduate,[2] but helped launch the left-wing journal, Forward, in 1906, and in the same city later became associated with the 'Red Clydesiders', a socialist grouping that included James Maxton and Manny Shinwell.

He was re-elected for Stirling and Clackmannan Western at the 1929 general election, when he was appointed Under-Secretary of State for Scotland by Prime Minister Ramsay MacDonald.

This troubled administration was relatively short-lived; only a handful of Labour ministers supported MacDonald's proposal of a coalition government, with Johnston and other Red Clydesiders among the strong opponents.

When many coal miners were unable to pay their premiums during the 1926 British general strike, the society remained supportive, in line with its founding principles; according to Johnston: On 10 October 1932, almost 20 years after joining the board, Johnston was appointed deputy and successor to James Stewart, the son of the society's original founder.

In 1941, Tom Johnson was appointed wartime Secretary of State for Scotland by Prime Minister Winston Churchill but continued to work for the society and the principles for which it stood.

When Sir William Beveridge was asked to make a report on industrial assurance, Tom Johnston came back to the campaign he had been waging among the members of the Association of Collecting Friendly Societies.

Responding to the Beveridge Report, a letter to the Association of Collecting Friendly Societies from David White, the interim general manager of the society, reiterated the need to remove some of the unnecessary costs of Industrial Assurance: The letter goes on to remind the Association of the attempts by Tom Johnston to get a sub-committee appointed.

In April 1939, during the build-up to the Second World War, John Anderson, the Home Secretary, appointed Johnston as Commissioner for Civil Defence in Scotland.

In this role, Johnston oversaw preparations for aerial bombardment and possible invasion, and the organisation of shelter and relief work.

He set up 32 committees to deal with any number of social and economic problems, ranging from juvenile delinquency to sheep farming.

There were coal-fired steam-turbine and some diesel-driven power stations serving urban locations, and excess capacity from a few large industrial hydroelectricity stations (e.g. those serving the aluminium smelters at Foyers and Kinlochleven) was made available locally, but there was no widespread distribution of electricity through a comprehensively integrated electric power transmission system such as the present National Grid.

[9] Possibly inspired by the earlier example of the American Tennessee Valley Authority initiative of the New Deal administration of President Franklin D Roosevelt, but undoubtedly determined to address the very strong popular sentiment of the immediate post-war period for a more equitable distribution of the resources and benefits of a modern economy, Johnston strove hard and successfully to win over all interested parties, including generally reluctant landowners, to the goal of harnessing the (then) scarcely developed but naturally well-suited geography and climate of the Scottish Highlands to the generation of electricity by water power.