The 23-year-old No8 joined Bordeaux when Wasps went into administration in October, but has now signed a long-term deal to switch to north London.
New England boss Steve Borthwick is giving serious consideration to selecting Willis alongside older brother and flanker, Jack, in his Six Nations squad.
Willis’s return to England for next season makes his selection easier to ratify under RFU regulations of only picking overseas players in extreme circumstances.
Willis’s Saracens switch leaves Billy Vunipola’s future up in the air, though. Saracens could struggle to fit Vunipola into their financial framework for next term after Willis’s capture. Vunipola is not short of lucrative offers from France and Japan. Rugby director Mark McCall hailed Saracens’ latest coup in recruiting Willis.
He said: “He is a player we have admired for a long time and we are confident he will be a huge success.”
England have special dispensation to select players based abroad who moved overseas after losing their jobs. There is no guarantee this will continue after the World Cup in France later this year, however.
“I’m incredibly excited to be joining Saracens,” said Willis. “It’s a great club with a fantastic playing and coaching group and I’m looking forward to being a part of it next season.”