"I had the pleasure of working with Kris when I was in charge at Saracens," said executive director of sport Steve Diamond.
"He has a great work ethic, is good in the lineout and is a very tough, uncompromising player. He has been playing well for Toulon since his move to France last year. This is another piece of my jigsaw completed with lots more signings to come."
Chesney joins recent signings Tony Buckley, Joe Ward, Kearnan Myall, Vadim Cobalas and Mark Easter as Diamond re-shapes the club's playing personnel.