Professor William Thelwall Thomas MBE, ChM, FRCS (February 1865 – 10 September 1927) was a Welsh surgeon who worked in Liverpool.

His father made a series of photographs of Thomas that are now in the collection of the National Library of Wales.

[1] Thomas attended school at the Liverpool Institute and studied medicine at the University of Glasgow where he graduated in 1886.

In 1913 he was elected professor of Regional Surgery at the University of Liverpool, a position he held until his retirement in 1927.

[2] He pioneered the use of antiseptic techniques in Liverpool, following the principles of Joseph Lister to which he had been exposed as a student in Glasgow.