Nothing is known of Dafydd himself apart from the very few facts which can be gathered from his poems. It appears that he had visited all parts of Wales: he knew Gruffudd Gryg of Anglesey and Madog Benfras of Maelor. He sang to Newborough in Anglesey, visited the cathedral at Bangor, and eulogized the dean, Hywel ap Goronwy. Men and women of noble birth in Ceredigion were also the subjects of eulogies by him. It has been generally supposed that Dafydd's chief patron was Ifor ap Llywelyn, or Ifor Hael (q.v.), of Bassaleg (now in Mon.). As the result of recent researches, however, it has been suggested that the poems to Ifor, although attributed to Dafydd ap Gwilym in all the manuscript sources, are the work of another poet, Dafydd Morgannwg. Dafydd ap Gwilym was buried at Strata Florida, and the yew tree growing over his grave was the subject of a cywydd by Gruffudd Gryg (q.v.).

Like many another nobleman of the time, Dafydd had completely mastered the art of the Welsh bards, and the craftsmanship of his poems links him with the highly skilled bardic tradition which had been evolved during the time of the Poets of the Princes. In his awdlau there are some extremely complicated syntactical formations. Most of his works are in the cywydd metre, which was the popular vehicle of the poets of the 14th cent., but even here the involved style of the Poets of the Princes is evident in all the well authenticated poems. They contain all the compound expressions, the parentheses, the archaic grammatical constructions and vocabulary which were at the time regarded as indispensable to a competent and dignified poetic style. It is true that he wrote some simpler poems, with loose cynghanedd, but in all the poems which are metrically highly developed he employs the traditional mode of expression. A large number of cywyddau have been wrongly attributed to Dafydd, and many such were included in Barddoniaeth Dafydd ab Gwilym, 1789, but even when all these have been eliminated there still remains a sound core of fine poems.

Dafydd is remarkable in his age for the large number of poems which he wrote about nature and about love. In this respect he far exceeded all his contemporaries, not only in amount but also in inspiration. It has been shown that he was influenced by the popular poetry of other countries, with which he probably became acquainted through sojourning among the mixed company which gathered in the towns, such as Newborough and Newcastle Emlyn. But Dafydd soars far above all influences. His view of the world around him is that of a true poet, and it is the true poet's sensibility which gives expression to it all in concrete images. His conception of the unity of the poem as the ordered production of a single mood is not matched in the works of any other Welsh poet until the present century. To communicate his vision he had the skill of one who was supreme master of the Welsh language, its vocabulary, and its terseness of idiom, and also of all the strict metrical rules of his time.