Taumalolo is notable the only forward in the 21st century to be awarded the Dally M Medal other than Danny Buderus and Cameron Smith.

Enrolled in primary school under his given name, Vaai, his teacher was unable to pronounce it correctly, instead deciding to call him "Jason".

[4] He grew up in Māngere and started playing rugby league at the age of 4 for the Papakura Sea Eagles and attended De La Salle College[5] along with older brother Warner.

At age 12, he moved to Townsville after being scouted and signed to a scholarship by the North Queensland Cowboys while playing for a touring New Zealand under-16 team.

He starred for the Cowboys in Round 25 against the Cronulla-Sutherland Sharks, coming off the interchange bench for the 3rd time to score two crucial tries and making two line breaks and 125 metres.

[14] Taumalolo played in the Cowboys in the NYC grand final against the New Zealand Warriors, scoring a try in the golden point 31–30 loss.

[23] Taumalolo was a standout in the Intrust Super Cup in the 2013 season, playing for Cowboys feeder club, the Mackay Cutters.

Taumalolo was selected in the 23-man New Zealand Test squad for the Baskerville Shield series but later withdrew due to injury.

[35] In the pre-season, Taumalolo again played in the Auckland Nines,[36] and was a member of the Cowboys' World Club Challenge winning side, starting at lock in the 38–4 victory over the Leeds Rhinos at Headingley Stadium.

The outfits, including Kansas City, then offered Taumalolo the opportunity to inspect their set-ups in the strongest sign of an NFL future.

On 1 October, he started at lock in North Queensland's 2017 NRL Grand Final loss to the Melbourne Storm.

[45] Following another strong season, in which he averaged 177m per game, Taumalolo was awarded the Paul Bowman Medal for Cowboys' Player of the Year for the third straight time.

[48] In Round 1 of the 2019 NRL season, Taumalolo ran for a career-high 301 metres in the Cowboys' 24–12 win over the St. George Illawarra Dragons.

On 18 September, he won the Paul Bowman Medal for Cowboys' Player of the Year for the fourth straight season.

[58] In February, Taumalolo was the captain of the Cowboys' 2020 NRL Nines winning squad and was named in the Team of the Tournament.

[63][64] On 3 October, Taumalolo won the Paul Bowman Medal for the fifth consecutive season, beating Johnathan Thurston's record of four wins.

North Queensland would finish the 2021 NRL season in 15th position on the table narrowly avoiding the Wooden Spoon.

[68] In the third group game at the 2021 Rugby League World Cup, Taumalolo scored two tries and was awarded man of the match in Tonga's 92-10 victory over the Cook Islands.

[70] Taumalolo played 23 games for North Queensland in the 2024 NRL season as they finished 5th on the table and qualified for the finals.