Stewart was second on the top try scorer list with 21 tries for the 2006 NRL season, one behind the South Sydney Rabbitohs' winger Nathan Merritt. In his first representative match playing for the Prime Minister's XIII against Papua New Guinea, he contributed to Australia's 28–8 win with a try. He made his State of Origin debut in Game 2 of the 2007 series, replacing injured Anthony Minichiello at late notice, and scored a try. Stewart played in the 2007 NRL Grand Final for Manly against the Melbourne Storm, and was knocked out while contesting a bomb with Storm forward Michael Crocker in the early minutes of the 2nd half. Stewart was selected as fullback for Australia's end of season test against New Zealand in Wellington, and contributed with a try in Australia's record 58–0 victory over the Kiwis.