The defender, 23, who played six matches during a short loan spell at the New York Stadium this season, has signed a two-year deal with the Millers.
Rotherham boss Steve Evans told the club's official website: "I think he's been absolutely sensational since he's joined us.
"He's salt of the earth, and he wants to come and work. He wants to improve, and for me he will play in the Championship one day, and he's only 23 now, so we hope that it will be with Rotherham United."
- Sports & Recreation