As a politician, he is best remembered for his long struggle to hold the mainly Welsh-speaking constituency of Carmarthen for the Labour Party against Plaid Cymru leader Gwynfor Evans, about which he wrote a book in the Welsh language.

In 1970, at the age of 27, he was elected Member of Parliament (MP) for Carmarthen, defeating the president of Plaid Cymru, Gwynfor Evans, with a majority of 3,600 votes.

When, in 1975, Prime Minister Harold Wilson held a referendum on Britain's membership of the European Economic Community (EEC), Jones was the Campaign Organiser in mid/west Wales for a 'Yes' vote.

Jones, alongside former MP William Edwards and future MPs Ron Davies and Ann Clwyd unsuccessfully sought the Labour nomination for Ogmore ahead of the 1979 general election.

At the merger debate in Sheffield during February 1988, Jones referring to Owen's refusal to join the SDP in a merged party with the Liberals was famously reported as telling delegates "you can't change British politics on the basis of hero worship.

When the contractual arrangements for the administration of school inspections were changed by the Welsh Government and Estyn from September 2012 the company ceased trading.

His eldest son, Glyndwr Cennydd Jones, was Plaid Cymru's candidate for the Merthyr Tydfil and Rhymney constituency for the National Assembly for Wales general election in May 2007.

He was particularly supportive of the 'Rainbow Alliance' proposals, which aimed to form a joint administration in Cardiff between Plaid Cymru, the Liberal Democrats and the Conservatives in 2007, being disappointed at the eventual formation of a Labour/Plaid coalition for the Assembly term 2007-11.

[11] He rejoined the Liberal Democrats in 2011, citing Nick Clegg's courage in entering a coalition in Westminster,[12] but was also known to have said at the time "I understand why it is happening but no good will come of it."