Thwaites was ordained priest on 2 January 1698, and shortly afterwards was elected fellow and lecturer of his college, to teach Anglo-Saxon.
The difficulty which he found in procuring sufficient copies of William Somner's Anglo-Saxon Dictionary (1659) led to the issue of another edition, with additions by Thomas Benson, in 1701.
Hearne speaks of Thwaites as reduced by 1711 to a skeleton; he was suffering from a complication of disorders, and Charles Bernard, royal surgeon, was impressed by his heroism during an operation to amputate his leg; he is said to have mentioned the case to Queen Anne, who made a grant of money.
His first project seems to have been to edit, with a commentary and translation, King Alfred's Anglo-Saxon version of the Universal History of Orosius, and this plan had Hickes's approval.
The coins described were from the collection of Sir Andrew Fountaine, another Oxford contemporary, friend, and fellow contributor to Hickes's Thesaurus.
[6] In 1711 Thwaites returned to Anglo-Saxon, dedicating to his old pupil, Christopher Rawlinson, his Grammatica Anglo-Saxonica, ex Hickesanio Linguarum Septentrionalium Thesauro excerpta (Oxford).