The 24-year-old England international becomes the first man to go down what could become a well-trodden path with the Super League club and Premiership champions announcing details of a link-up which incorporates co-operation between the respective coaching teams and academies, player loans and a cross-code match.
Tomkins' move represents quite a coup for Sarries, who benefited from the player's desire to try his luck in rugby union.
He said: "I will always be a proud Wiganer, but everybody in rugby union and rugby league can see there is something very special happening at Saracens, and I can't wait to be part of it."
Wigan chairman Ian Lenagan added: "Joel wished to move to the south of England and take his chance at rugby union.
"Wigan would not step in the way of a player with such clear ideas to leave. He is joining an excellent club in Saracens.
"Wigan has grown close with Saracens through these and previous discussions and we are delighted and excited by the partnership between Wigan and Saracens we are announcing today.
"Both games have their own place separately but the synergy available from these two leading clubs working together is exceptional."
Saracens chairman Nigel Wray said: "Wigan are a fantastic rugby club with a fantastic worldwide reputation, and we are really excited by the potential of this partnership as we share resources and knowledge to ensure each club is able to maximise its potential on and off the field."
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