[1][2][3] He won gold medal with the New Zealand team in the men's rugby sevens tournament during the 2018 Commonwealth Games.

He was also a key member of the New Zealand side which won the 2018 Rugby World Cup Sevens tournament by defeating England 33-12 in the final.

[4] He was named in the New Zealand squad to compete at the 2020 Summer Olympics in the men's rugby sevens tournament.

Knewstubb was named as a late signing for Tasman during the 2021 Bunnings NPC after a season-ending injury to Mark Tele'a.

He made his debut for Tasman against Bay of Plenty at Trafalgar Park in a non competition match, starting in the number 15 jersey and scoring a try in a 26–9 win for the Mako.