Born in Liverpool, the son of John and Elizabeth Thomas, and was educated at the Liverpool Institute. He became a medical student at Glasgow and received the triple diploma in 1886 after obtaining a part of his medical education at Liverpool. Sir Mitchell Banks (qv) made him Demonstrator of Anatomy, and he then served as Assistant to a general practitioner in Wales, returning after a short period to hold the offices of House Physician and House Surgeon at the Royal Infirmary, Liverpool. He was elected Holt Tutorial Scholar in Anatomy and Derby Exhibitioner at University College, Liverpool, in 1887, where he was Assistant Lecturer and Demonstrator of Anatomy. Lecturing at first upon practical surgery in the University, he was elected Professor of Clinical Surgery in 1918, held office until 1922, and then became Emeritus Professor, the honorary degree of ChM having been conferred upon him in 1909. He settled in Hope Street, Liverpool, in 1890, determined to practise surgery apart from general practice, and maintained himself by 'coaching' students. In 1890 he was elected Assistant Surgeon to the Royal Infirmary, became full Surgeon in 1907, and retired in 1923. At the Royal College of Surgeons of England he was on the Council from 1921 until his death. At the British Medical Association he was Hon Secretary of the Section of Surgery at the Belfast Meeting in 1909, General Secretary at the Liverpool Meeting in 1912, and President of the Surgical Section at the Brighton Meeting in 1913. He was also President of the Liverpool Medical Institution for the year 1918-1919, and represented the University of Liverpool on the General Medical Council in succession to Dr Richard Caton from Jan 2nd, 1926. He was one of the founders of the Provincial Surgeons' Travelling Club which went from centre to centre at home and abroad to observe advances in the practice of surgery. He married in 1892 Anabel, daughter of Alexander Spence, of Huntly, Aberdeenshire. She died without children after a painful illness in July, 1927, and her death accelerated his own. Thelwall Thomas died suddenly whilst reading in his study at Allerton, Liverpool, on Sept 10th, 1927. He left estate valued at £109,759, and bequeathed £5000 to the University of Liverpool to endow a fellowship in surgical pathology; £5000 to the Royal College of Surgeons of England, and £5000 to the Royal Medical Benevolent Fund for pensions for medical men and their widows. A portrait painted by subscription in 1925 is in the possession of the University of Liverpool. He also appears in the portrait group of the Council painted by Moussa Ayoub in 1928. Thelwall Thomas was a fine surgeon, and is reported to have been the most dexterous operator in Liverpool since the days of Edward Bickersteth (qv); he was equally skilled in diagnosis. Brought up at Glasgow with those who had been taught by Lister, he was largely responsible for establishing a surgical technique of the highest order in the operating theatre of the Royal Infirmary, and with F T Paul he was a pioneer there of abdominal surgery. In surgery he introduced the detempered needle, the black silkworm gut, and the large-handled Spencer Wells forceps. He perfected the operation for haemorrhoids by suture over the face of a clamp, and in 1903 introduced the transverse incision in the operation for the cure of umbilical hernia. He was much interested in the surgery of the kidney, was responsible for the introduction of the double incision for calculi when they occur simultaneously in the kidney and distal end of the ureter, and made an important investigation into the chemical constitution of renal calculi. As a man he was friendly, generous, and hard-working.