Dalyell was born in England but raised in the family home (The Binns) in Edinburgh, his father was an "old school" Empire civil servant and through his mother he is a hereditary baron. He was educated at Eton College. He was a soldier with the Royal Scots Greys from 1950 to 1952 for his national service. He then went to King's College, Cambridge to study history and economics, where he ran the Conservative Association. Unusually, he then trained as a teacher at Moray House College in Edinburgh and taught at a non-selective school and a ship school. He joined the Labour Party in 1956 after the Suez. He has been a MP since June 1962, when he defeated William Wolfe of the SNP in a hard fought by-election contest for West Lothian. From 1983 onwards he has represented Linlithgow (basically a renaming of his West Lothian seat) and has easily retained his position as their representative since then. He has been the Father of the House since the 2001 General Election, after Sir Edward Heath retired. He was a MEP from 1975 to 1979, and a member of the Labour National Executive from 1986 to 1987 for the Campaign group.
Dalyell is outspoken in Parliament and true to his own views. His stance has ensured his isolation from significant committees and jobs. His early career was promising and he became parliamentary private secretary (PPS) to Richard Crossman. But he annoyed a number of ministers and was heavily censured by the privileges committee for a leak about the biological weapons research establishment Porton Down to the newspapers (though he claimed that he thought the minutes were in the public domain). When Labour failed to hold power in 1970 his chances of senior office were effectively over. He was opposed to Scottish devolution and first stated the famous "West Lothian question", although the name was given by Enoch Powell. In this he was wildly out of touch with the people of Scotland. He continued to argue his own causes: in 1978 to 1979 he voted against his own government over 100 times, despite a three-line whip.
Dalyell is vocal in his disapproval of military action and 'imperialism'; from his opposition to action in Borneo in 1965 he has contested almost every British action - arguing against action in Aden, the Falklands War (especially the sinking of the General Belgrano), the Gulf War and action in Kosovo and Iraq, saying, "I will resist a war with every sinew in my body". He was also a strong presence in Parliament concerning the Lockerbie bombing and Libya. He is pro-Europe.
He has a genuine interest in science and has been a columnist for New Scientist magazine since 1967.
On March 7, 2003 Dalyell was elected Rector of Edinburgh University by the staff and students. His term of office will be three years.