Tomkins joins the Super League champions with immediate effect for an undisclosed fee, signing a contract until the end of 2018.
He was presented to the crowd during the half-time interval of Wigan's 48-4 defeat of Widnes on Wednesday.
The 27-year-old played three Tests for the England rugby union side in 2013.
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"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 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, who made his Wigan debut as an 18-year-old, joined Saracens at the end of the 2011 season, shortly after scoring a stunning try in the Challenge Cup final win over Leeds.
He is currently recovering from a back injury and is not expected to be fit for about four weeks.
His decision to return to rugby league is a boost for the sport, after England international Sam Burgess switched codes and agreed a move to Bath for next season.
Tomkins's younger brother Sam swapped Wigan for NRL side New Zealand Warriors at the end of last season, after helping the club to a Super League and Challenge Cup double.
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The National League club's ground is undergoing refurbishments this summer.
The Hive, home of Barnet, hosted Arsenal for the 2017 Spring Series as a new pitch was laid at Meadow Park.
"We're delighted to continue our long-standing relationship and pleased to contribute to these improvements," said Arsenal club secretary David Miles.
Boreham Wood chairman Danny Hunter told his club's website: "This long-term partnership and a grant from the Premier League, through the FSIF (Football Stadia Improvement Fund), have helped us to undertake an incredible range of Premier League-type ground improvements."
Meanwhile, former WSL 1 champions Arsenal have given a new deal to Netherlands international goalkeeper Sari van Veenendaal.
The 27-year-old, who joined the Gunners in 2015, has agreed an undisclosed-length contract with Pedro Martinez Losa's side.
Dual-code international Joel Tomkins has returned to rugby league side Wigan Warriors after a three-year spell in rugby union with Saracens.
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Arsenal Ladies have agreed a deal to continue playing their home games at Boreham Wood's Meadow Park home until 2027, along with Arsenal's youth teams.