The 27-year-old, who will join the Cherry and Whites with immediate effect for an undisclosed fee, was presented to the crowd during the club's 48-4 victory over Widnes Vikings last night.
"I'd like to thank Saracens for the opportunity to try a different sport, a different lifestyle and also for assisting my development which allowed me to represent my country," Tomkins told Wigan's official website.
"However, after a long thought-out process and at this stage in my life, I realised that the timing was right to come home.
"I am very grateful to Wigan Warriors for taking me back to the best rugby club in the world. It means everything to me to pull on the famous cherry and white jersey again."
Tomkins made his Wigan debut as an 18-year-old, before joining Saracens at the end of 2011.