In 2011, Paasi played for the Warriors Toyota Cup Under-20s team. On 5 October 2011, Paasi played in the Warriors' 2011 NYCGrand Final victory over the North Queensland Cowboys, playing off the interchange bench in the Warriors' 31-30 golden point extra time victory. On 6 October 2011, Paasi was named 18th man for the Junior Kiwis. In 2012, Paasi moved on to the Warriors New South Wales Cup team, the Auckland Vulcans, and he also played for the Vulcans in 2013. At the start of 2014 Paasi wasn't contracted to any NRL team but was given a chance to play in the Warriors pre-season games, earning a contract with the Warriors NSW Cup side.
2014
After a few impressive performances in the NSW Cup, Paasi was handed his NRL debut for the New Zealand Warriors in Round 19 against the Brisbane Broncos, where he played off the interchange bench in the Warriors 28-22 loss at Suncorp Stadium. This was Paasi’s only first grade match in the 2014 season. He was named as the Warriors NSW Cup Player of the Year. In November, Paasi signed a train and trial contract with the Gold Coast Titans, starting from 2015. On 16 October, Paasi played for Tonga against Papua New Guinea, starting at second-row in the 32-18 loss in Lae.
2015
In Round 1, Paasi made his club debut for the Gold Coast Titans against the Wests Tigers, playing off the interchange bench in the Titans 19-18 loss at Cbus Super Stadium. In Round 4 against the Cronulla-Sutherland Sharks, he scored his first career try in the Titans 24-22 win at Remondis Stadium. Paasi’s good form in the Titans early matches earned him a 2-year contract extension with the Titans. He finished his impressive year with him playing in 18 matches and scoring 2 tries.
2016
In February, Paasi was named in the Titans 2016 NRL Auckland Nines squad, where he was named in the Team of the Tournament. He was described as, "undoubtedly the weekend’s biggest surprise packet" and perhaps the best player of the Nines. Paasi enjoyed a solid 2016 NRL season with him playing in all the Titans 25 matches and scored 5 tries.
2017
Paasi’s 2017 NRL season was limited due to a shoulder injury, playing in 11 matches for the Titans. On 5 November 2017, Paasi was released from his final year of his contract with the Titans to join his former club the New Zealand Warriors on a 2-year deal, starting from 2018. 2019 In Round 24 2019, Paasi played his 100th NRL game in the Warriors 10-31 defeat by the South Sydney Rabbitohs at Mt Smart Stadium in Auckland.