Sainsbury was selected as part of Australia's 2015 AFC Asian Cup squad. He started in Australia's first group game against Kuwait, a match which Australia won 4-1. He also started Australia's second group game against Oman, providing the assist for Matt McKay to open the scoring in a 4-0 win by heading a Massimo Luongo corner goalwards. Sainsbury scored his first ever international goal in the semi-final against the United Arab Emirates. Under three minutes into the game, he headed a corner from Massimo Luongo in at the far post to give Australia the lead in a match they ultimately won 2–0. He also played for Australia in the Final victory over South Korea and was named as Man of the Match following an imposing defensive display. Trent was named in the official team of the tournament after a number of solid performances.