In 1936, with two others, Lewis was involved in an arson attack on an air force base at Penrhos, for which he was imprisoned, losing his lecturing post as a result. The sequence of events raised his personal profile and that of Plaid Cymru. He continued to write, becoming a prominent literary and political figure, and in 1952 was given a senior lectureship at Cardiff. After his retirement in 1957, he continued to express militant views, lending his support to Cymdeithas yr Iaith Gymraeg. In 1970, he was nominated for the Nobel Prize for Literature. His works include nineteen plays, poetry, novels and essays. He wrote mostly in Welsh but also in English. By the time of his death, he was the most celebrated of living Welsh writers.