Locke, 25, will link up with the Red Devils at the start of next season, having made 87 appearances for the Warriors in the NRL.
Salford coach Iestyn Harris said: “There is no doubt in my mind that next year we will have the most exciting full-back in the competition.
“Anybody who has seen Kevin play will have seen how fast he is but his game is more than raw pace. He is a class act and he will light up Super League for at least the next three seasons, of that I am sure.”
Owner Dr Marwan Koukash revealed the signing on Twitter earlier today, and says the club will be announcing another player in the next 72 hours.
“This signing proves that we will be competitive at the very top of the sport.”