Wainui has died in a car crash near Tauranga on Monday morning.
The crash happened just before 8am at McLaren Falls Park, with the 25-year-old dying at the scene as the sole occupant of the vehicle.
Chiefs and Māori All Blacks coach Clayton McMillan said Wainui's death was a huge loss.
"Sean was an incredibly talented individual and held a great amount of mana among his fellow teammates and the wider rugby community.
"He epitomised everything you could possibly ask for in a player. He will be remembered for being a passionate, hard-working, proud Māori who was an exceptional player but more importantly father and husband.
"He was an influential member in the teams he has been a part of, and his presence will be missed."
Wainui joined the Chiefs in 2018 and played 44 games for the Super Rugby franchise, have previously played for the Crusaders.
He was first picked for the Māori All Blacks in 2015 and made ten appearances for them.
Of Ngāi Tūhoe, Ngāti Porou, Ngā Ariki Kaipūtahi and Te Āitanga a Māhaki iwi, he was also a vocal advocate for Te Reo Māori, proud of his heritage and passionate about his whānau.
New Zealand Māori Rugby Board Chair Farah Palmer said rugby was mourning one of its Rangatira.
"Our first thoughts are with Sean's whānau. They have lost a father, a husband, a brother and a son and we share their grief and their tears.
"As a player we all saw what this young tāne was capable of and the passion and talent that he brought to the teams he represented, but we also saw a role model for young Māori, a caring father who was passionate about his culture, his language, and his identity.
"He will be sorely missed."
Wainui was born in the small settlement of Whatatutu near Gisborne and raised in Auckland, before attending Takapuna Grammar School where he was a stand-out as captain of the first XV.
He made his debut for Taranaki in 2014, while still a teenager and a year later won the Junior World Championship with the New Zealand under-20 team.
Wainui earned his first Super Rugby contract with the Crusaders, before joining the Chiefs in 2018 and becoming a fan favourite either in the midfield or on the wing.
Earlier this year, he broke the record for number of tries in a Super Rugby game with five against the Waratahs.
New Zealand Rugby (NZR) chief executive Mark Robinson said it was a dark day for rugby, extending condolences to Wainui's wife Paige, their children Kawariki and Arahia, and their wider whānau.
"We offer them our full support at what is the most difficult of times.
"We know Sean's passing will be felt deeply by everyone involved in rugby, particularly his Bay of Plenty and Chiefs teammates, and we share their sorrow and their shock."