Nigel John Spearing was born in Hammersmith, London on 8 October 1930, the son of Austen Spearing, a Liberal parliamentary candidate, and his wife May. Spearing was educated at the independent Latymer Upper School in Hammersmith. He became a member of the Congregational Church (later United Reformed Church) in 1947. Following National Service in the Royal Signals, he went up to read Geography at St. Catherine's College, Cambridge. On graduation in 1956 Spearing became a geography tutor at Wandsworth School, and rose to become head of its geography department. He left in 1968 to become a housemaster at Elliott School, Putney. He married, in 1956, Wendy Newman, with whom he had one son and two daughters.

Spearing joined the Labour Party in 1953, and the National Union of Teachers in 1955. He served as chair of Labour's Barons Court constituency party, 1961-63, and on the Hammersmith Local Government Committee, 1966-68. During this period, Spearing unsuccessfully contested several local council elections in London and the safe Conservative parliamentary seat of Warwick and Leamington at the 1964 general election. In 1966 he was co-opted as a member of the Greater London Council's planning and transport committees. In 1968 he also became director of the Institute of Community Studies' Thameside Research and Development Group. A critic of plans for the new Thames Barrier, he published 'The Thames Barrier-Barrage Controversy' with the Institute in 1969.

In 1970, Spearing retired from teaching and was elected Labour MP for Acton in that year's general election. Three months after defeat in the 1974 general election, he won a by-election in Newham South and represented the constituency until it was abolished under boundary changes ahead of the 1997 general election.

During his time in parliament Spearing was a conscientious constituency MP and a member of a number of select committees, including those for overseas development, procedure, sound broadcasting, and foreign and Commonwealth affairs. He devoted most energy to the European Legislation Scrutiny Committee, on which he served as a member from 1979 to 1997, becoming its chair between 1983 and 1992. From 1989 to 1997 he was also chair of the Labour Party's parliamentary affairs committee. A moral conservative, he opposed longer pub opening hours, supported greater protections for the unborn, and denounced the introduction of market forces into the National Health Service.

In 1997, Spearing became a vice-president of the Campaign for an Independent Britain (CIB), the cross-party lobbying organisation opposing the United Kingdom's continuing membership of the European Union. This issue was to occupy him for the rest of his life. He had long been a vociferous parliamentary opponent of European integration, having been the last Opposition MP to speak in the debate before the vote was taken to pass the European Communities Act in 1972. He campaigned to protect the interests of workers at Tate & Lyle's Silvertown refinery when the UK's membership of the EEC supplanted the Commonwealth Sugar Agreement, and went on to chair the CIB.'s Eurosceptic predecessor, the British Anti Common Market League, from 1977 to 1983. He was also a member of the Labour Common Market Safeguards Committee, later the Labour Euro-Safeguards Campaign, and Chairman of the Anti-Maastricht Alliance.

A keen cyclist and rower, Spearing maintained a passionate interest in public transport, particularly improvements to the national rail network and safety on the London Underground, as well as the capital's waterways and flood defences. He was president of the Socialist Environment and Resources Association, 1977-1986. While MP for Newham he campaigned against the Conservative government's London Docklands Development Corporation, and in 1998 became joint president of the London Dockland Forum. From 1975 to 2008 he was also a vice-president of the River Thames Society.

Spearing died after a long-term fight with Alzheimer's on 8 January 2017.