 A Hearts supporter Edinburgh-born Thomson began his career playing for Loanhead Boys Club before joining Hearts Youth Academy, signing a professional contract with the club in July 2003.He was selected for the Lothian Schools XI in 2002 while a pupil at Beeslack High School (Penicuik), along with other Hearts youngsters John Armstrong, David Gray and Andrew Driver.Thomson earned an unexpectedly early debut in March 2005, when a flu epidemic at Tynecastle forced Hearts' head coach John Robertson into naming a plethora of youngsters in his first team squad against Inverness Caledonian Thistle.