His father died at an early age and Thomson resided with his mother and elder brothers James and William in Russell Square.

One of his first postings as a professional was at Grantham Golf Club where he stayed only a short time before returning to the West Links.

[2] Thomson compiled an excellent playing career that included numerous caps for Scotland for the Home International Team from 1903–12, except the 1908 match which was cancelled due to inclement weather.

[2] In a tournament at Walton Heath Golf Club in 1904 he qualified for the match play competition in which he dispatched Harry Vardon 1 up.

Thomson led with 75 after reaching the turn in 34, a shot ahead of amateur John Graham, Jr. and Harry Vardon.