At age 17, Paasi moved to Australia on a scholarship to play for Keebra Park State High School where they won the Arrive Alive Cup in 2009.

[14] On 16 October, Paasi played for Tonga against Papua New Guinea, starting at second-row in the 32-18 loss in Lae.

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.

[24][25] In Round 24 2019, Paasi played his 100th NRL game[26] in the Warriors 10-31 defeat by the South Sydney Rabbitohs at Mt Smart Stadium in Auckland.

[31] On 9 October, he played for St. Helens in their 2021 Super League Grand Final victory over Catalans Dragons.

[32] On 24 September, Paasi played for St Helens in their 2022 Super League Grand Final victory over Leeds.

[33] On 18 February, Paasi played in St Helens 13-12 upset victory over Penrith in the 2023 World Club Challenge.

[35][36] Paasi played 16 matches for St Helens in the 2024 Super League season which saw the club finish sixth on the table.