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

Thomas was born in Liverpool in 1865, the son of the Welsh photographer John Thomas (1838–1905) and his wife Elizabeth. 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.^[1]

Thomas decided to devote himself to work as a consultant surgeon to the exclusion of other medical work; this was unconventional at the time. He was appointed as an assistant surgeon at the Liverpool Royal Infirmary in 1892 and as a full surgeon there in 1907. In 1913 he was elected professor of Regional Surgery at the University of Liverpool, a position he held until his retirement in 1927.^[1]

Thomas became president of the surgical section of the British Medical Association in 1913. He was on the council of the Royal College of Surgeons from 1921 until his death.^[2]

Thomas was a fine and dexterous surgeon who was equally skilled at diagnosis.^[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.^[3] He developed what is still the most common surgical treatment for varicose veins.^[4] The first planned appendectomy in Liverpool was performed by Thomas in 1895.^[5]

Thomas spoke Welsh fluently and maintained a close interest in Welsh affairs. In 1925 he was one of the presidents at the National Eisteddfod in Pwllheli.^[1]

Thomas was an active member of the Welsh Calvinistic Methodist Church (now the Presbyterian Church of Wales) and was for many years a Sunday school teacher.^[1] He was the medical officer of the Foreign Mission of the Presbyterian Church of Wales.^[6]

In 1892 he married Anabel Spence; they had no children. Anabel died in 1927, two months before her husband on 10 September 1927.^[3]

List of Welsh medical pioneers

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