On 26 February, Tupou extended his contract with the Roosters to the end of the 2015 season. He became a full-time first grader in 2013, scoring 14 tries from 26 games. His most impressive try came in the 2013 NRL Grand Final when he leapt over Manly's David Williams to level the game at 6-6. Roosters went on to win the Grand Final 26-18 against the Manly-Warringah Sea Eagles. Tupou was named in the 24-man Tongan 2013 Rugby League World Cup squad. He made his Tongan international debut against Scotland on the wing in the 26-24 loss at Derwent Park. Tupou played in all of Tonga's 3 matches in the tournament.