Turnbull played for Caledonia under-16 and under-18 and Scotland under-18A and under-18. He also represented his country at basketball in the under-16 and under-18 groups.[1] He was named Scotland Under-19 Player of the Year at the Scottish Rugby Awards Dinner in May 2006.[1] Injury prevented his participation in other shadow Six Nations matches until the final game against France in March 2007.[1]
He joined Edinburgh as a full-time professional during the summer of 2008 after graduating from the National Academy.[1] He made his debut two years previously as a replacement in the draw with Connacht in the Celtic League match in Galway in September, and his first start followed two months later against Cardiff Blues at Murrayfield.[1]
Turnbull formed a lock partnership with Richie Vernon in Scotland's four under-19 internationals in season 2005–06, before going on to play in four matches in the age group's world championship in Dubai.[1] He added to his international honours by playing in the under-20 match against England at Bath in February 2007.[1]
