[1] Thompson was born in Brisbane, Queensland to a farming family from North-West Tasmania who moved to Sydney, New South Wales when he was a child.

[2][3] He grew up playing rugby union as a contemporary of Wallaby Phil Waugh at Sydney Church of England Grammar School.

In 2010, Roberts-Thomson continued his strong form and with Craig Bolton suffering a serious Achilles tendon injury early in the year, he and Heath Grundy stepped up manfully to take on the brunt of the defensive work.

For Roberts-Thomson, 2011 was an up and down year as injury and the rapid improvement from Ted Richards and Alex Johnson didn't allow for him to take up his normal position as a tall defender.

Illness to Grundy allowed Roberts-Thomson to take up a position in the backline late in the year however, a role that he would fill well for the Swans' run into the finals.