Taranaki Upon leaving school, Wainui was contracted by the
Taranaki Rugby Football Union. In his first year out of school he was a part of Taranaki's 2014 national provincial championship squad. He was spotted by coach
Colin Cooper and had signed with Taranaki at just 18-years-old after an impressive season, not only for his
New Plymouth Old Boys club but for the
Chiefs development side also. Wainui made his debut for
Taranaki in the
2014 ITM Cup competition, coming on as a replacement against
Waikato. In the following year, he recorded nine appearances, including 5 starts, and scored three tries for the province in
Super Rugby matches. Overall, between 2014 and 2020, Wainui made 49 appearances for Taranaki and scored 15 tries.
Crusaders In 2015 he was signed by the
Super Rugby franchise the
Crusaders after impressing in the centre and wing position for Taranaki. Wainui made his debut for the Crusaders in round one of the
2016 Super Rugby competition, starting in the
outside centre position against the
Chiefs.
Chiefs Prior to the
2018 Super Rugby season, he signed with the
Chiefs. By the end of the
2021 Super Rugby season, he made 44 appearances for the club and has scored 18 tries. On 12 June 2021, in a 40–7 victory over the
Waratahs during
Super Rugby Trans-Tasman, he became the first player in Super Rugby history to score 5 tries in a single match. ==International career==