Walton, who was born at Dungarvan in Ireland, studied at the Methodist College, Belfast, where he excelled at mathematics and science. In 1922 he entered Trinity College, Dublin, graduating in mathematics and experimental science in 1926.

In 1927 he went to Cambridge University on a research scholarship and worked in the Cavendish Laboratory under Ernest Rutherford. It was here that he performed experiments, together with John Cockcroft, with accelerated particles. The experiments were to lead to the two men sharing the 1951 Nobel Prize for physics for “their pioneer work on the transmutation of atomic nuclei by artificially accelerated atomic particles,” more commonly known as “splitting the atom.”

In 1934 Walton gained his PhD from Cambridge and returned to Dublin as a fellow of Trinity College. He was appointed Erasmus Smith Professor of Natural and Experimental Philosophy in 1946 and was elected a senior fellow in 1960. In 1952 he became chairman of the School of Cosmic Physics of the Dublin Institute for Advanced Studies, where he remained until retiring in 1974.