Duffie attended Saint Kentigern College in Pakuranga, Auckland, New Zealand, where he was a part of the school's First XV, playing at fullback.

[4] He is the first Kaiapoi (now Northern) Bulldogs junior to be selected for the New Zealand national rugby league team.

[6] Melbourne Storm scout Darren Bell discovered Duffie playing rugby union and offered him a scholarship.

Duffie made his first-team debut against Harlequins RL at the Twickenham Stoop in the World City Challenge in 2010.

[11] In April 2011, Duffie signed a three-year extension to his contract with the Storm, taking him to the end of the 2014 season.

[15] Following this, Duffie tore the anterior cruciate ligament in his left knee and re-injured his right shoulder whilst playing for the Cronulla Sharks in round 5 of the New South Wales Cup competition.

On 19 February, Duffie collided with a teammate during a training session and injured the same knee from 2013, rupturing his left anterior cruciate ligament.

Duffie was subbed off in the 65th minute after colliding with the Lions' replacement back Liam Williams twice during the match.

Duffie made his debut for New Zealand in the 31–22 win over the Barbarians on 4 November 2017, as a replacement off the bench for in-form winger Waisake Naholo in the 67th minute.