Beer was born in London. He started a degree in philosophy at University College London, but left in 1944 to join the army. He saw service in India and stayed there until 1947, he was demobbed in 1949 having reached the rank of captain.
He had become aware of operational research while in the army and he was quick to identify the advantages it would bring to business. He joined United Steel and persuaded the management to found an operational research group, the Department of Operations Research and Cybernetics, which he headed. In 1959 he published his first book Cybernetics and Management, building on the ideas of Norbert Wiener, Warren McCulloch and especially William Ross Ashby for a systems approach to the organisation management.
Having gained experience he left United Steel in 1961 to start an operational research consultancy in partnership with Roger Eddison called SIGMA (Science in General Management). Beer left in 1966, poached by the SIGMA client International Publishing Corporation (IPC). Beer was made development director at IPC and pushed for the adoption of new computer technologies. Also in 1966 he wrote Decision and Control. He left IPC in 1970 to work as an independent consultant, reflecting his growing interest in social systems.
His biggest independent project was never completed, he was approached by the socialist government of Chile in 1971 to develop an entire real-time computerised system to run the social economy. When Pinochet took power in 1973 the project was abandoned. Beer continued to work in the Americas, consulting for the governments of Mexico, Uruguay and Venezuela. He also wrote a series of four books, based on his own Viable System Model for organisation modeling - Platform for Change, Designing Freedom, Heart of Enterprise and The Brain Of The Firm.
In the mid 1970s Beer renounced material possessions and moved to mid-Wales where he lived in an almost austere style, he became interested in poetry and art. From the 1980s he established an alternative home in Toronto. he still worked in his field and in 1994 published Beyond Dispute: The Invention of Team Syntegrity. Team Syntegrity is a formal model built on the polyhedra idea of systems for non-hierarchical problem solving.
He was a visiting professor at almost thirty universities and received a honorary doctorate from the University of Sunderland. He was president of the World Organization of Systems and Cybernetics and holder of awards from the Royal Swedish Academy for Engineering Sciences, he United Kingdom Systems Society, the American Society for Cybernetics, and the Operations Research Society of America.
He was married twice, in 1947 to Cynthia Hannaway and in 1968 to Sallie Steadman. He had five sons and three daughters.