After schooling at King Edward's School, Birmingham, he went up to Trinity College, Cambridge in 1885, graduating with a first class degree in both classics and Indian languages and being awarded a Browne medal in both 1888 and 1889.
[1] At Cambridge he studied Sanskrit under the influential Orientalist Edward Byles Cowell.
[2] Thomas collaborated with Jacques Bacot in publishing a collection of Old Tibetan historical texts.
In addition he studied many Old Tibetan texts himself which were collected in his four-volume Tibetan literary texts and documents concerning Chinese Turkestan and Ancient folk-literature from North-Eastern Tibet.
His catalogues of the Tibetan manuscripts from Central Asia brought to the India Office Library by Marc Aurel Stein remained unpublished until 2007, when his catalogue of Tibetan manuscripts from Stein's third expedition was published on the website of the International Dunhuang Project.