[1] Thomson was born at Fahan (pronounced 'Fawn'), a village in Inishowen in County Donegal on the north coast of Ulster, the northern province in Ireland, the seventh child of the five sons and three daughters of John Gibson Thomson of Ardrishaig, Argyllshire, Scotland, civil engineer, a pupil of Thomas Telford, and his wife Catherine, a daughter of John Sinclair of Lochaline House, Morven, Sound of Mull.

[2] Thomson went on to work at Queen Charlotte's Hospital and as a surgeon on ships operated by Union-Castle Line on routes to South Africa.

Famous laryngologists he visited in Vienna included Leopold von Schrötter and Karl Stoerk, along with the Austrian otologist Ádám Politzer.

After obtaining the further qualification FRCS (Fellow of the Royal College of Surgeons), he lectured in medicine, carried out research, and helped edit the journal The Laryngoscope.

His home in Wimpole Street in London, kept by his elder sister Matilda (Maud) Louisa Sinclair-Thomson, housed his collection of Shakespearian prints, miniatures and pharmacy jars.