Donnelly was chosen to fight Pembrokeshire for the Labour Party in the 1950 general election, which a good Labour candidate had narrowly failed to win in 1945 and where the sitting Member, Gwilym Lloyd George, was very popular, not merely because he was the son of David Lloyd George.
In Parliament, he defined himself as "an Englishman with an Irish name sitting for a Welsh seat"[REF] and initially allied with Aneurin Bevan.