 He contested the Glasgow Govan constituency at the 1959 general election, then the 1962 West Lothian by-election; Glasgow Govan again at the 1966 general election.He became the National Organiser of the CPGB in 1966, and while holding this post, contested elections in St Pancras North at the 1970 and February 1974 general elections.In 1975, McLennan was elected as General Secretary of the Communist Party of Great Britain.