He was educated at Trinity Academy, Edinburgh, at the time a selective state school, and then Heriot-Watt University, where he attained a BA in economics.

After leaving university, he worked as an insurance clerk and then became active in the Scottish Union of Students, including serving as its president from 1970 until 1971.

He was shadow defence secretary and later was Chairman of the Trade and Industry select committee.

[3] O'Neill served as Chairman of the Strategic Forum for Construction and the Nuclear Industry Association.

O'Neill was also a patron of Humanists UK,[5] and was one of the fifty signatories to a letter published in The Guardian in 2010, which called for Pope Benedict XVI not to be given a state visit to the UK, and accused the Catholic Church of increasing the spread of AIDS and promoting segregated education.