The 24-year-old made 21 league and cup appearances for Rochdale last season.
"We fought very hard to get this one done. He's played in midfield so he's very combative, but we feel right-back is his best position," boss Adam Murray told the club website.
Bennett is Mansfield's fifth summer signing following Danny Rose, George Taft, Ashley Hemmings and CJ Hamilton.
The length of his contract has not been disclosed, and the deal will be completed on 1 July.
Mansfield Town have signed former Rochdale defender Rhys Bennett on a free transfer.