Evans studied at the University of Wales, Aberystwyth, and at St John's College, Oxford, from where he qualified as a lawyer. During his time at St John's, he became a member of the Dafydd ap Gwilym society there. He was also a market gardener. He was a teenager when the Welsh nationalist party Plaid Cymru was founded in 1925, and he founded a branch of the party while he was at Oxford. He became the party's president in 1945 and retained the office until 1981.