Born near Glasgow, Gardner worked in a brass foundry at the age of fourteen.
Gardner was highly active in the ILP during World War I, but then joined the Communist Party of Great Britain (CPGB) on its formation in 1920.
[1] The Associated Iron Moulders eventually became part of the National Union of Foundry Workers, and Gardner was elected as its Scottish district secretary in 1941, succeeding Jock McBain.
[1] He stood in the election to become general secretary of the Foundry Workers in 1943 and, despite the opposition of the union's executive, lost to the incumbent Albert Wilkie by only 7,044 votes to 8,024.
[1] In 1944, Wilkie died and Gardner stood again for the general secretary post, this time beating Tom Colvin in another close vote.