The 23-year-old joins the Red Devils after a successful season with the Hornets which saw him become a regular in the first team helping Rochdale to Championship survival.
Hornets Coach Alan Kilshaw took Bennion to the Crown Oil Arena at the beginning of the 2017 season Where he became a pivotal forward for Rochdale.
Bennion enjoyed loan spells with Swinton Lions and Featherstone Rovers before signing for Halifax in 2016 from Warrington. The Red Devils newest acquisition has also played for Intrust Super Cup side Mackay Cutters in Australia.
Head Coach Ian Watson said: “Through our good relationship with Alan Kilshaw, we’ve been keeping tabs on Gavin throughout the 2017 season and he’s put in some massively impressive performances for Rochdale.
“He’s a young, hungry forward with a great work ethic and excellent attitude and we believe he can grow into a quality Super League player.
“I first came across Gavin at Warrington where he showed plenty of potential. Gavin then choose to go across to Australia to help with his rugby education where he was selected for the Queensland residents team.
“Gavin has shown his development this year while working with Alan at Rochdale and hopefully he can continue that here at Salford Red Devils. I’m excited to work with him next season and I feel he’ll prove to be a good signing for Salford.”
Red Devils CEO Ian Blease said: “Gavin is the first of a few signings we’re hoping to announce in the coming weeks and months.
“We feel he’ll be a great addition to the squad, and under Coach Watson’s guidance I’m expecting Gavin to challenge for a first team position at the start of the new season.
“Gavin is the first of a new batch of Red Devils who we feel can help continue our growth on the field in 2018.”