A switch to rugby union had been a possibility for the full-back, who is England's all-time leading try scorer.
Sam's Super League story
Scores five tries on Wigan Warriors debut in Challenge Cup tie against Whitehaven.
Named in Super League's Dream Team for the first time. Scores three tries on international debut for England against Wales.
Scores in Grand Final win against St Helens as Wigan claim their first title since 1998. Equals England record for tries in a single Test match, crossing four times against France.
Plays in Wigan's Challenge Cup win over Leeds Rhinos at Wembley. Signs new five-year contract on the same day his older brother Joel swaps codes to join Saracens. Makes first rugby union appearance, playing on the wing for Barbarians against Australia at Twickenham.
Wins League Leaders' Shield with Wigan. Ends season with 36 tries and is voted Super League's Man of Steel for the first time. Becomes England's all-time leading try scorer.
Equals club record by scoring in 11 consecutive matches for Wigan. Scores last-minute try in Wigan's Challenge Cup final win against Hull FC at Wembley. Named in Super League's Dream Team for fifth year in succession.
Wigan, who have also announced that full-back Matt Bowen, 31, has joined from North Queensland Cowboys as a direct replacement, will have first refusal to sign Tomkins if he chooses to return to Super League in the future.
"This has been a very difficult decision to make but it is now perfect timing for me to make the switch to the NRL," said Tomkins. "It is something in my career I have always wanted to do and this agreement with the Warriors also allows me to return back to Wigan in the future.
"I head to New Zealand with some great memories of Grand Final and Challenge Cup success and some very special times.
"Going to Auckland is a huge step for me and my rugby league career but one I am really looking forward to. I want to end my time with further success with Wigan as we aim for Grand Final glory, and then with England as we focus on winning the World Cup on home soil."
Wigan head coach Shaun Wane said he was excited for Tomkins, describing the full-back as a "great kid".
"For all his plus points, the main one is that he's competitive," Wane told BBC Radio 5 live. "The Warriors will get someone who wants to win and he'll be very vociferous in the changing room.
"He's one of my leaders. They'll get a competitive player who will challenge the coaching staff because he wants to get better. They have a fantastic player in Sam Tomkins."
Among his domestic honours are two Challenge Cup final victories (2011 and 2013) and a Super League Grand Final win (2010), while he is also England's all-time leading try scorer with 16 in 15 appearances.
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