Born into a Plymouth Brethren family in Lumphinnans in Fife, Moffat left school at the age of fourteen to work at the local coal mine.
After joining the Communist Party in 1922, he helped publish the `Buzzer', a newsletter for militant miners at Glencraig Colliery, Lochgelly.
[14] During World War II, Moffat served as a sergeant in the Royal Corps of Signals, remaining a councillor but attending meetings during periods of leave.
It included the presence of the Scottish Miners Youth contingent, a rally and procession, a pipe band and competitions.
[4] He was the mineworkers' representative on the general council of the Scottish Trades Union Congress, and served as its president in 1959.
[18][19] He was the CPGB's candidate for the presidency of the National Union of Mineworkers in 1960, and led the voting until the final round, when he was narrowly beaten by Sidney Ford.
[20] He succeeded Abe as president of the Scottish Mine Workers in 1961,[4] beating future Member of Parliament Alex Eadie in the election.