Duffy first appeared in February 2011 at the Junior World Championships in Courmayeur . There he won the bronze medal with the relay over 3000 m. He made his debut in the World Cup in February 2012 in Dordrecht and finished 22nd in the 1500 m. In the 2014/15 season he achieved his first podium finish in the World Cup in Shanghai with third place in the relay. Also in the season he came second in the relay in Seoul and third in Erzurum over 1000 m. His best placings at the 2015 World Championships in Moscow were 11th place over 1000 m and seventh place with the relay over 5000 m. He finished the season in eighth place in the 1000 m World Cup. At the beginning of the 2015/16 season he won his first World Cup victory with the relay in Toronto . This was followed by three third places in the relay in the World Cup. In the following season he came in six World Cup starts twice under the top ten, including third place over 1000 m in Gangneung .
Canada
