 He was a teacher at Durham University, Director of Studies of the Co-operative College, Workplace Director of Alcohol Concern, member of Commission of Industrial Relations, Workers' Educational Association, and European and International Consultant on workers rights, economics and security.O'Brien was elected Member of Parliament for Darlington in the March 1983 by-election following the death of Edward Fletcher.In the general election held just three months later, he lost the seat to the Conservative party candidate Michael Fallon, who had been his rival in the by-election.