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Boyd, who coached the Hurricanes their maiden Super Rugby title in 2016, has signed a three-year deal with the English club, it was announced on the Saints official website.
"I'm passionate about the Hurricanes and making the call not to carry on was a tough one, but the opportunity at Northampton presented an exciting new challenge that was too good to pass up," Boyd said.
"With my coaching future now decided I can fully focus on the 2018 season and making sure my final year is a memorable one."
Boyd said he was looking forward to the move.
"I am humbled and excited to be joining Saints," Boyd said. "Northampton Saints is a Club I have admired all of my coaching career.
"I visited Franklin's Gardens for a week in 2004 when Wayne Smith was head coach, and remember the passion of the Saints supporters and the strong culture at the Club.
"The Club's ambitions match my own – I am confident I can help the Saints become one of the biggest and best teams in Europe.
"I have always aspired to coach in the Aviva Premiership and I am relishing the opportunity to work with this talented squad of players."
The 59-year-old has been head coach of the Hurricanes since 2015 and was previously in charge of the New Zealand Under-20s.
In three seasons in charge of the Hurricanes, the side have a 43-11 record and have reached the playoffs each time, including two trips to the final.
Hurricanes Chief Executive Avan Lee said Boyd's successor would be announced in due course.
"I think the main thing right now is that with Boydy's plans for 2019 confirmed everybody's collective focus will be solely on 2018 and giving the Hurricanes the best possible chance at another title," he said.
Lee said Boyd's place in Hurricanes folklore was assured after he led the club to its first Super Rugby title in 2016.
"Boydy's done a great job and we are sad to see him go, but we understand Northampton is a great opportunity for him and we'll be wishing him all the best when he heads away."