"At the same time I am indebted to the Storm organisation which has been brilliant in every respect, and helped develop me to the player I am today.
"I have a rugby background but more importantly I think that the skill set to play at wing or fullback in rugby league is very similar to rugby."
The Blues said Duffie is an excellent signing to step into the shoes of the departing All Black Charles Piutau.
"Matt is a fantastic athlete, and was a highly promising young rugby player," said Umaga. "He has developed into an excellent professional rugby league player at fullback and wing and that experience in those positions fits ideally to the role of an outside back in rugby.
"We are very excited to have him join the Blues, not just for his playing ability but as someone who has played top level professional sport for a highly successful organisation. He is also a leader who will add real direction to our young backs."
Duffie has signed for an initial two years and will play his ITM Cup rugby for North Harbour where he will re-link with Matt McGahan, who also played for the Storm, and good friend Bryn Hall, the Harbour captain.
"He is a marquee signing for the Blues and for Harbour," said North Harbour coach Steve Jackson. "We are excited to have him join us as a player and as a leader.
"If we can get everyone on the field at once, then a backline in 2016 with the likes of Ahki, Ranger, Duffie, McGahan, Li and Tuitavake is very exciting."
Duffie has had his share of injuries with the Storm including a shoulder reconstruction and two ACL operations but Umaga said the former Kiwi international had passed the stringent medical examinations.
He learned rugby at Pakuranga before the family moved to North Canterbury for two years where he mixed rugby and rugby league as a young teen. He returned north to attend St Kentigern College where he proved an outstanding athlete.
He played for the New Zealand ARL team at 16 and was a national secondary schools finalist in athletics in the 200m, 400m and long jump. He was invited to trial for the national volleyball team and played premier touch before he was spotted by the Melbourne Storm and moved to Melbourne at 18.