[10] Less than a month after his 16th birthday, Opetaia travelled to Kazakhstan to compete in the 2011 Junior World Championships and would win the gold medal in the light heavyweight division by defeating Germany's Melvin Perry 5:3 in the final.

[12] In February 2012, still aged 16, he travelled to Hobart to compete in the 2012 Australian Olympic qualifying tournament where he would win the gold medal in the heavyweight division.

A month later he competed in the Oceanic Olympic qualifying tournament held in Canberra and once again emerged victorious in the heavyweight final by defeating New Zealander David Light 15:10.

[14] In the lead up to the 2012 Olympics, Opetaia travelled to Armenia to compete in the heavyweight division of the AIBA Youth World Boxing Championships and claimed the bronze medal, losing a close 11:9 semifinal to eventual gold medalist Andrey Stotskiy from Russia.

[15] A month after his 17th birthday, he travelled to London to compete as the youngest boxer in the heavyweight division of the Olympics and was controversially defeated in the first round 12:11 by eventual bronze medalist Teymur Mammadov from Azerbaijan.

[24] Opetaia fought Navosa Ioata for the vacant WBA Oceania interim cruiserweight title on May 15, 2019, and won the fight by an eight-round technical knockout.

[37] Opetaia was expected to face mandatory challenger Mateusz Masternak in early 2023, but was forced to undergo left shoulder surgery on February 1, 2023.

The IBF removed Masternak's mandatory status the very next day and ordered Opeteia to face the #2 ranked cruiserweight contender Richard Riakporhe instead.

[45] This allowed Opetaia to enter into negotiations with Jordan Thompson for a voluntary title defense that took place at the Wembley Arena in London, England on September 30, 2023.

[48] During the fight week's early stages, Opetaia vacated the title when the IBF, the sanctioning body, insisted on a mandatory defense against former champion Mairis Briedis, who was recovering from an injury.

[52] Opetaia was expected to face Mairis Briedis for the vacant IBF cruiserweight championship on the undercard of Tyson Fury vs. Oleksandr Usyk.

The fight was initially expected to take place on February 17, 2024, at the Kingdom Arena in Riyadh, Saudi Arabia,[53] but the entire event was later postponed after Tyson Fury suffered a facial injury in training.

[56][57] Opetaia made the first defense of his IBF cruiserweight title during his second reign against Jack Massey at Kingdom Arena in Riyadh, Saudi Arabia, on 12 October 2024, winning by stoppage in round six.