[4] In 2017, he followed in his brother Bailyn Sullivan's footsteps and moved to Auckland where he spent his final two years of secondary school at King's College.
[19] Sullivan went on to play 7 games for the Blues in his first season, which culminated in the franchise winning the Super Rugby Trans-Tasman title.
[22] In 2018, after his last year at King's College, Sullivan was named in the New Zealand Secondary Schools team for a three-match international series in Australia.
[24] A year later, Sullivan - who is of Ngāti Kahungunu descent - was selected to play for the first ever New Zealand Māori Under 20 team in a match against Fiji.
[28][29] In June 2022, Sullivan and his brother Bailyn were – for the first time – named in the Māori All Blacks squad to take on Ireland on their New Zealand tour.