After playing in the lower grades at the Knights, Pangai Junior joined the Canberra Raiders in 2013 and played for their NYC team from 2013 to 2015. On 7 November 2013, he re-signed with the Raiders on a 3-year contract. On 18 October 2014, he played for the Junior Kangaroos against the Junior Kiwis, playing at second-row in the Kangaroos' 14–15 loss at Mt Smart Stadium. He was again selected for the Junior Kangaroos in May 2015, playing off the interchange bench in the Kangaroos' 22-20 win at Robina Stadium. On 12 September 2015, he was named in Tonga's 58-man train-on squad for the World Cup qualifier against the Cook Islands. Two days later, he was named at second-row in the 2015 NYC Team of the Year.
2016
In January, Pangai Junior signed a 2-year contract with the Brisbane Broncos starting in 2017, however, in February, he was granted a release from the final year of his Raiders contract to join the Broncos effective immediately on a revised contract for just the 2016 season. On 7 May, he played for the Junior Kangaroos against the Junior Kiwis for a third year in a row, starting at prop and captaining the side in the Kangaroos' 34-20 win at Parramatta Stadium. In Round 12 of the 2016 NRL season, he made his NRL debut for the Broncos against the Wests Tigers, playing off the interchange bench in the Broncos' 19-18 loss at Suncorp Stadium. In his next match in Round 13 against the New Zealand Warriors, he scored his first NRL career try in the Broncos' 36-18 loss at Mt Smart Stadium. He finished his debut year in the NRL having played in 14 matches and scoring 2 tries for the Broncos in the 2016 NRL season. On 22 September, he re-signed with the Broncos on a 2-year contract until the end of 2018.
2017
After the Broncos local derby clash against the much weaker opponent, Gold Coast Titans in Round 7 as they won effortlessly with a 24-22 win at Suncorp Stadium, Pangai Junior suffered a finger injury during the match and was sidelined for a number of weeks. Pangai Junior would return from injury in Round 13 against the Sydney Roosters in the 18-16 loss at Sydney Football Stadium. Pangai Junior finished the 2017 NRL season with him playing in 18 matches for the Broncos. On 5 October 2017, Pangai Junior was selected in the 24-man squad for Tonga for the 2017 Rugby League World Cup. On 11 November 2017, Pangai Junior made his international debut for Tonga against New Zealand, coming off the interchange bench in the inspirational 28-22 shock win at Waikato Stadium. Pangai Junior would play in the next match for Tonga against Lebanon in their 24-22 win at AMI Stadium in Christchurch. In Tonga’s Semi Final match against England, Pangai Junior scored his first international try, the start of an unlikely Tonga comeback from 20-0 down with 9 minutes to fulltime. As Tonga would dare to dream and score another two more 2 tries to make the score 20-18 with 2 minutes to fulltime, England winger Jermaine McGillvary lost the ball in his own half of the field, Tonga had one more final chance to pinch a stunning victory but unfortunately would end up in tears after Andrew Fifita would go over the tryline on the fulltime siren but the try wasn’t checked by the video referee when the ball was raked out of his hand by England second-rower Elliot Whitehead but was seen by referee Matt Cecchin as a knock on, the match ending in a thrilling fashion 20-18 at Mt Smart Stadium. Pangai Junior finished the exciting tournament with him playing in 3 matches and scoring 1 try.
2018
After showing a good performance in Round 1 against the St George Illawarra Dragons as the Broncos lost 34–12 at Jubilee Stadium. In Round 2 in the Queensland derby match against the North Queensland Cowboys, Pangai Junior had a monster performance, scoring a try out of sheer strength, nearly scoring a second identical try but was disallowed and making a very crucial try saving tackle on Cowboys forward Scott Bolton as he ran to score under the posts from a inside ball from Johnathan Thurston but was slammed into the goalpost by him in the 78th minute and the Broncos came on top as 24–20 winners at Suncorp Stadium. As Pangai Junior showed himself as the standout forward for the Broncos, he was under consideration for the New South Wales State of Origin squad, but he opted to stay loyal to Tonga to represent his family but later didn’t take part in the Pacific international against Samoa due to injury. After missing a couple of matches due to injury in Round 19 against the Penrith Panthers, Pangai Junior had a sensational first half, scoring 2 tries as the Broncos went on to win convincingly 50-18 at Suncorp Stadium. Pangai Junior would finish his best season to date, playing in 22 matches and scoring 5 tries for the Broncos. On 20 October, he played in the historical first-ever Test match between Tonga and the Australian Kangaroos, scoring a try in the 34-16 loss at Mt Smart Stadium, playing in front of a sold-out crowd at Mount Smart Stadium, Auckland. In late November, Pangai Junior announced that he wanted to represent New South Wales for the 2019 series, after being named in Brad Fittler’s 32-man training squad. On 6 December 2018, Pangai Junior re-signed with the Broncos on a 1-year contract for the 2019 season, despite being offered lucrative contracts from other clubs.
