After spending much of his earlier life as a journalist, Jones joined the National Library of Wales at Aberystwyth in 1909; in 1913 he went to the University of Wales as lecturer and, later, as professor of Welsh literature.

His awdl “Ymadawiad Arthur” (“The Departure of Arthur”), which won the highest honour at the National Eisteddfod in 1902, is one of the most significant landmarks in the Welsh literary revival of the early 20th century. Critics have seen his greatest achievement in the poems Tir na n-Og, a lyrical play for performance with music; “Broseliawnd,” set in the forest of Broceliande; “Anatiomaros,” set in a district of ancient Gaul; “Argoed,” depicting an ideal community; and “Cynddilig,” a bitter protest against war written in the style of the Llywarch Hen cycle. His translations of Goethe's Faust (1922) and his collection of Greek poems and Latin epigrams, Blodau o Hen Ardd (1927; “Flowers from an Ancient Garden”), with H.J. Rose, are considered among the most successful renderings of literary classics into Welsh.