He was one of the leading figures of the Shop Stewards' Movement in wartime Glasgow (the 'Red Clydeside' period) and a founding member of the Communist Party of Great Britain.

[2] The "weakness for alcohol" shown by his father and elder brother, and the suffering that it caused his mother, led him to become involved with the Temperance movement in his mid-adolescence.

However, on discovering that colleagues had canvassed support for a director of a Trust Public House in the 1906 general election, Gallacher ended his association with the organised Temperance movement.

[3] A subsequent period as a member of the Independent Labour Party ended quickly, and he joined the Social Democratic Federation, which brought him into contact with John MacLean.

David Lloyd George and Arthur Henderson met Gallacher and the Clyde Workers' Committee in Glasgow, but they were unwilling to back down on the issue.

Glasgow was expected to be particularly badly affected because a large proportion of its workforce was employed in war-related areas such as munitions and shipbuilding, which would suddenly contract with the end of the war.

Revolution was the furthest thing from the minds of the trade union leaders of the day, but Gallacher later claimed that they should have marched to the barracks in the Maryhill district of the city and encouraged the Scottish troops there to leave them and join the workers against the government.

He led the grouping into the Communist Party of Great Britain (CPGB) and stood for election to the House of Commons at Dundee (both in 1922 and 1923), West Fife (1929 and 1931) and Shipley (1930).

[7] In an article published in the party's Labour Monthly in April 1953 he appraised the career of Joseph Stalin; the Soviet First Secretary had died the previous month, concluding with the assertion that "his life ended with his work completed, for the Party and the Soviet people still under his wise guidance will go forward, resolute as he was resolute—to the new truly free society of Marx and Engels, of Lenin and of Stalin".