[2][3] While still an undergraduate, Williams evinced his taste for Welsh research by winning, in 1831, a prize offered by the Cymmrodorion Society for the best "biographical sketch of the most eminent Welshmen since the Reformation".
In 1836 the English version was issued with additions (London, 12mo), and it was subsequently developed into Enwogion Cymru: A Biographical Dictionary of Eminent Welshmen (Llandovery, 1852, 8vo), which was then the best work of its kind relating to the principality.
In this lexicon copious examples with English translations are given from such Cornish works as are still extant, but its special feature was the addition of synonyms and cognate words from Welsh, Breton, Erse, Gaelic, and Manx.
He also discovered at Peniarth a previously unknown Cornish drama, being the Ordinale de Vita Sancti Mereadoci.
According to the Dictionary of National Biography, this, in spite of its great value, is perhaps the least satisfactory of Williams's works, as his reading of the text is not always to be relied upon.