In May 2013, Trent was selected in a Socceroos Australian-based training squad for upcoming World Cup qualifiers.
In July 2013, he made Australia's squad for the 2013 EAFF East Asian Cup.
Despite strong club form, Sainsbury was the only outfield player in the squad not to be used by coach Holger Osieck in the tournament, which he suggested may have been due to Osieck mistaking his laid-back attitude for a lack of commitment.

Sainsbury's chances of playing in the 2014 FIFA World Cup were ultimately ended by a knee injury suffered playing for PEC Zwolle.

In September 2014, Sainsbury made his International debut for Australia in a 2–0 loss to Belgium in a friendly.
He later admitted to having been nervous before the game but earned praise from coach Ange Postecoglou for his performance against a strong opponent.

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.

In May 2018 he was named in Australia's 23-man squad for the 2018 FIFA World Cup in Russia.
In May 2013, Trent was selected in a Socceroos Australian-based training squad for upcoming World Cup qualifiers. In July 2013, he made Australia's squad for the 2013 EAFF East Asian Cup. Despite strong club form, Sainsbury was the only outfield player in the squad not to be used by coach Holger Osieck in the tournament, which he suggested may have been due to Osieck mistaking his laid-back attitude for a lack of commitment.
Sainsbury's chances of playing in the 2014 FIFA World Cup were ultimately ended by a knee injury suffered playing for PEC Zwolle.
In September 2014, Sainsbury made his International debut for Australia in a 2–0 loss to Belgium in a friendly. He later admitted to having been nervous before the game but earned praise from coach Ange Postecoglou for his performance against a strong opponent.
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.
In May 2018 he was named in Australia's 23-man squad for the 2018 FIFA World Cup in Russia.
Trent Sainsbury