While at Bangor, Goronwy Roberts, together with Harri Gwynn was one of the founders of Mudiad Gwerin, a nationalist left-wing pressure group.

[1] He continued to represent the constituency until February 1974, when he lost his seat to Dafydd Wigley of Plaid Cymru.

During the 1950s, Goronwy Roberts was, together with Cledwyn Hughes and others, a stalwart of the Parliament for Wales campaign.

In 1951, Plaid Cymru announced that the party would not oppose him at the general election due to his support for the campaign.

When Labour lost power in 1970, he became an opposition spokesman on Foreign and Commonwealth Affairs.

[6] Goronwy Roberts was a strong supporter of devolution and of Welsh culture but was also a fierce critic of what he regarded as the nationalistic excess of Plaid Cymru.