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. He held on to the seat by just 3 votes (with five recounts) in the February 1974 general election, but lost the seat back to Evans by 3,640 votes in the October election of that year. When MP he was in 1974 Parliamentary Secretary to Rt Hon Roy Jenkins, the Home Secretary, and was also a member of the Council of Europe. Throughout his time in Parliament he campaigned for more devolution for Wales, an issue that split the Welsh Labour Party deeply.
In June 1974, in a letter to the Executive of the Carmarthen Constituency Labour Party, he warned of the dangers of the ever leftward drift of the party saying – I cannot any longer conceal my acute concern about some developments in the Labour Party which will in my view not enhance the prospects of the Labour Party and will also affect the longer term unity of the Labour Movement. I happen to believe strongly in the principles of Social Democracy. When in 1975, Prime Minister Harold Wilson held a referendum on Britain’s membership of the European Economic Community (EEC), Gwynoro was the Campaign Organiser in mid/west Wales for a ‘Yes’ vote.
During the period Roy Jenkins was in Brussels as President of the European Commission the two communicated on a very regular basis as how a new third force in British politics could be established.
In 1981 he helped establish the Social Democratic Party. Together with Tom Ellis, former MP for Wrexham, and others, he created a powerful Welsh voice within the UK SDP. Gwynoro Jones stood in the Gower by-election of 1982 when Labour's 19,000 majority was reduced to 7,000. He was Chair of the SDP in Wales for two three-year periods before the merger of the SDP with the Liberals. During the days of the SDP-Liberal Alliance he chaired its National Committee in Wales from 1983 to 1989. In the 1980s Gwynoro became a powerful advocate for constitutional and electoral reform, and was a renowned orator at conferences and public meetings across the UK. A strong advocate of the alliance with the Liberals, he was often at loggerheads with David Owen. At the merger debate in Sheffield during February 1988, Gwynoro 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 Liberal Democrat Party was formed he stood for the Presidency and received over 10,000 votes. He topped the poll in the vote for the party's National Committee and became vice chair of the Policy Committee. In 1992 he stood for the Hereford seat and received over 23,000 votes.
After that Gwynoro concentrated on his business activities, and from 1993 until 2012 was head of EPPC-Severn Crossing Ltd, a school inspection and conferencing business. During that period the company inspected over 10,000 educational establishments in England and Wales. Gwynoro visited some 1000 of Wales’s schools on inspections and regularly expressed concerns about standards in teaching, learning and performance. 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. In addition to being a Lay Inspector of schools he was also an Investors in People Adviser/Assessor, External Assessor Performance Management of Headteachers, External Assessor for EFQM European Business Excellence Model, Consultant/Assessor Law Society Lexcel Standard and Health Inspectorate Wales lay inspector.
He stood as an independent in the National Assembly elections of 2007 and was very supportive of the Rainbow Alliance proposals which aimed to form a joint administration in Cardiff between Plaid Cymru, Liberal Democrats and Conservatives - being particularly disappointed at the eventual formation of a Labour/Plaid coalition for Assembly term 2007 -11. He rejoined the Liberal Democrats in 2011, citing Nick Clegg's courage in entering a coalition in Westminster, but was also known to have said at the time - I understand why it is happening but no good will come of it. He soon became a critic of the way the coalition was operating and the damage it was doing to the party’s electoral prospects.
Following the UK General Election of May 2015, Gwynoro became active in politics again expressing his determination to do what he could to rebuild the party that he had actively helped to develop in the 1980s. He is an active blogger and has his own YouTube channel.] He was particularly saddened by the passing of Charles Kennedy and has been critical of Plaid Cymru's performance in the Welsh Assembly.
Gwynoro is a passionate European and is the Vice Chair of the Wales Council of the European Movement.