Born May 12, 1924, in Glasgow. Figure in the British working-class movement.
The son of a worker, McLennan joined the Communist Party of Great Britain in 1943 and took part in the Communist youth movement and the trade union movement. He became the head of the organizational department of the CPGB in Glasgow in 1949 and was subsequently named secretary of the CPGB organization there. He headed the Scottish division of the CPGB from 1957 to 1965.
In 1957, McLennan became a member of the Executive Committee of the CPGB; he was elected to the Political Committee of the Executive Committee that same year. Between 1965 and 1975 he served as secretary of the Executive Committee for party organization, head of the organizational department of the Executive Committee, and chairman of a subcommittee of the Executive Committee devoted to party work among youth. He was elected general secretary of the CPGB in March 1975.
McLennan is the author of several works dealing with the British and international Communist and working-class movements.