Fullarton represented Scotland at under 21, under 19 and under 18 levels and made 15 appearances for the Scotland A side. He made his full Scotland debut in their tour of New Zealand in 2000, replacing Scott Murray in the first Test against New Zealand, and was subsequently selected in the starting line up for the second test. He won his third cap, again as a replacement for Scott Murray in the November 2001 Test, also against New Zealand. He won his fifth cap for Scotland when he came on as a substitute in the 2003 Rugby World Cup countdown Test against Ireland in 2003. Earlier that summer he toured South Africa with Scotland but did not play in either Test match. Overall he won eight international caps. In 2009 Fullarton represented the Barbarians.