The powerful 28-year-old New Zealander, who stands 6ft 5in tall and weighs 14st 6lbs, can also play fly-half and full-back.
Wilson, who will arrive in time for the start of the new Premiershp season on September 1, said he had always wanted to play in England.
"Playing in the Premiership has always been a goal of mine and I can't wait to join Northampton Saints," he said.
"The history of the club is something that is very special, and the coaches and squad that I am joining are world class.
"I cannot wait to get out in front of the incredibly passionate fans that I have witnessed on TV and run out at Franklin's Gardens."
Saints director of rugby Jim Mallinder said: "James is an experienced player who has shown his abilities on both sides of the world.
"He reads a game well, brings other players around him into the play and has a strong kicking game too."
Gilbert has released a new line of rugby cleats. The Gilbert Virtuo 8S is part of the exciting new product. Check it out.
The entire All Blacks apparel line has been updated for 2013/14. Check out the New Zealand All Blacks polo.
The Nike Tiempo is a solid rugby cleat and one of few styles still made from full-grain natural leather.
The Gilbert Blitz 8S rugby cleat is a great cleat at a great price of $69.99. Get a new pair of cleats today.
A cool looking all black rugby cleat with the high performance adidas is known for. Get in the Gear!
Wear the crest of the British and Irish Lions on your t-shirt. A great look for the summer.
The All Blacks Performance t-shirt is black with hints of blue from the training jersey. Very Cool.
The New Zealand All Blacks training jersey for 2013/14. Get in the Gear!
The USA Rugby Pro Alternate rugby jersey is perfect for any fan of the Eagles. Get yours to wear during the summer Test matches.
The NEW All Blacks 2013/14 jersey has arrived at World Rugby Shop. Dare to wear the colors of the All Blacks.