Mr Thomson was born at Selkirk on 14th February 1868, the eldest of the nine children of a sheep farmer in the Border country; his school life began in Penicuik and was continued at St Andrew's School, Perth. He became a pupil-teacher, and then entered the Church of Scotland Training College in Edinburgh, where his ability in all subjects, particularly in mathematics, made him conspicuous.
While training at the College, he entered the University of Edinburgh, where he was First Medallist and Prizeman in the mathematical classes for three years in succession, and gained the Newton Bursary. In 1891 he graduated with First Class Honours in Mathematics and Natural Philosophy; among those who obtained the same degree at the same time were M E Philip, afterwards one of H M Inspectors of Schools in Scotland, and A Mitchell Hunter, who was ordained to the Ministry of the Free Church of Scotland and became Librarian of New College. He was awarded the Vans Dunlop post-graduate scholarship in mathematics, and also won an open scholarship to Caius College, Cambridge, where he took up rowing with distinction. In the Mathematical Tripos of 1894 he was bracketed 15th Wrangler.
On leaving Cambridge he entered the teaching profession, and, after some experience in Kirkwall and at Kilmarnock Academy, was appointed in 1899 to succeed Mr J W Butters in the mathematical department of George Heriot's School, Edinburgh. Here, until his retirement in 1928, he trained a long succession of boys who made their mark in the University and in later life.
He married in 1898. Mrs Thomson died in 1936, and a son and daughter survive.
He was a good chess player and musician, and a member of the Choral Union Society's Choir, being present at their practice only a week before his death. He spoke many languages fluently, was a member of the Norwegian Club, and with the Norwegian Pastor founded the Scandinavian Choir. He was also a keen gardener and fisherman, and was a member of the Trout Angler's Club for many years. To the last, he had a great zest for life, and he is mourned by a wide circle of friends.