His publications are very numerous. He published the following works which were translated by him from the English originals: Ymarferol-Waith i'r Elusen Ysgolion, yn egluro Natur Conffirmasiwn mewn ffordd o Gwestiwn ac Atteb. Gyda nifer o Weddiau cyfaddas i'r Achos arbennig hwnnw , 1711 , and Boreol a Phrydnawnol Weddi i Deulu , 1711 (both by Robert Nelson ); Llawlyfr y Llafurwr ( Edward Welchman ), 1711 ; and Cydymmaith i'r Allor ( William Viccars ); while in Archaeologia Britannica ( Edward Lhuyd ) will be found ‘ An Armoric Grammar and Vocabulary by Julian Manoir English'd out of French by M. Williams .’ He edited the S.P.C.K. Bible together with the Book of Common Prayer in 1718 , and a second impression of both in 1727 , and in 1730 edited Cyfreithjeu Hywel Dda ac eraill, seu Leges Wallicae Ecclesiasticae & Civiles Hoeli Boni et aliorum Walliae Princium … Notis & Glossaris illustravit Gulielmus Wottonus . He edited and published William Baxter (q.v.) of Llanllugan 's Glossarium Antiquitatum Britannicarum , 1711 ; Reliquiae Baxterianae , 1726 , and a second impression of this work in 1731 under the title Glossarium Antiquitatum Romanarum ; The Breviary of Britain , Humphrey Lhuyd , 1723 ; and Britannicae Descriptionis Commentariolum , Humphrey Lhuyd , 1731 . He also published Y Namyn un deugain Articlau Crefydd , 1710 ; Cofrestr o'r Holl Lyfrau Printjedig , 1717 ; Proposals for Printing by Subscription a Collection of Writings in the Welsh Tongue to the beginning of the Sixteenth Century , 1719 ; Repertorium Poeticum , 1726 ; and Orders relating to the Almshouses … of Devynog , 1731 . He intended publishing a new edition with additions of The Historie of Cambria ( David Powel , q.v. ), an edition of Juvenal 's satires, and of Edward James 's Llyfr yr Homiliau . He did not achieve his ambition of producing an enlarged edition of John Davies of Mallwyd 's dictionary and grammar although, as his manuscripts show, he had begun the work of collecting the material and editing it. His collection of ‘Triads,’ prepared for the press in 1717 , remains in manuscript, and so does his dissertation ‘ A Chronological Account of the Several Editions of the Scriptures in Welsh ,’ his catalogue of the contents of the Bodleian library , and his ‘ Llech o'r Holl Brydyddion Cymreig .’ The response to his ‘ Proposals ,’ published in 1719 , was disappointing and he had to abandon his ambitious and praiseworthy intention.

He rescued scarce books . He travelled all over Wales , visiting the mansions of the great in order to inspect their libraries and to copy or take extracts from their manuscripts. The Llanstephan manuscripts and the Shirburn printed books, now in the National Library , are ample proof of his industry and that of his father, Samuel Williams . He was a worthy disciple of Edward Lhuyd , for he was, and still is, acknowledged to have been one of the greatest of Welsh scholars. It is not, therefore, surprising that he won the friendship and esteem of the greatest English scholars of his day, men like William Wotton , John Hudson , Thomas Hearne , and Humphrey Wanley .