Born December 20th 1931, as Samuel Alexander Barr, he began working in the shipyards of the Clyde as an apprentice welder with Charles Connell and Company in Scotstoun when he was 15 years old. He became shop steward for his fellow apprentices before taking up the same role for the welders in the Boilermakers' Society.
A Communist from his youth he was elected on to the party's Scottish committee at a young age with the support and encouragement of Finlay Hart who was his mentor. In the 1960s, he was a Communist candidate for local council elections for Partick West.
In his 40s, he became closely associated with Jimmy Reid and Jimmy Airlie over their joint leadership of the UCS work-in during 1971-2.
A Boilermakers' Society shop steward at UCS for many years, he was written about by Tony Benn in 1969, two years before the UCS occupation. The then Minister for Technology, Benn, recorded in his diary on March 14 1969 details of the stormy meeting he had held in Glasgow with the UCS shop stewards: "It was pretty tough and there were a few shouts. One guy called Sam Barr, a Communist shop steward, said they simply wouldn't accept redundancies."
In 1977 he ran for the office of assistant general secretary of the Boilermakers Society, topping the poll in the first round, only to be beaten in the run-off. Sammy Barr stood for Parliament in Glasgow Garscadden three times in February 1974, a by-election of 1978, and in 1979.
He was a long term delegate to Glasgow Trades Council executive from the early 1980s becoming its vice-chairman.
As an Executive Committee member of the Communist Party in the1970s and early 1980s, he stayed with the CPGB until 1991.
His union merged with the GMB, thus after retirement, he was president of the retired members' association for the GMB until he died on May 7th 2012 and a GMB branch secretary in Glasgow right up until his death.