He served with the Royal Scots Fusiliers as a machine-gunner during World War I, eventually becoming a non-commissioned officer, but was invalided out with malaria in 1918.
The CPGB decided to oppose the split and, although Proudfoot remained prominent in the Reform Union, he agitated for it to reunite with the Miners' Association.
The two Fife miners unions voted to reunify, and Proudfoot won election as a full-time miners' agent, alongside his comrade John McArthur - this despite union leader William Adamson calling three successive ballots in the hope of obtaining a different result.
[1] Frustrated with inactivity at the NUSMW, and encouraged by the Third Period policy of the CPGB to form separate unions, Proudfoot was a founder of the new, communist-led United Mineworkers of Scotland (UMS) and worked as full-time organiser for its Fife affiliate.
He retired from work and his political posts early in the 1950s as his health declined, and spent the last five years of his life unable to leave his bed, due to pneumoconiosis.