The 27-year-old, who has five England caps, was in his second spell with Wigan after a stint with NRL side Parramatta Eels.
Mossop is the Red Devils' fourth new signing for next season after Daniel Murray, Kriss Brining and Lama Tasi.
"He adds depth to our pack and brings with him plenty of experience," said head coach Ian Watson.
Salford Red Devils have signed Wigan Warriors prop Lee Mossop ahead of the 2017 Super League season.