The 27-year-old featured 22 times last season for the Sky Blues and has now put pen to paper on a one-year deal after originally taking time to ponder his options.
Boss Tony Mowbray is ready to build his team around Johnson for the forthcoming Sky Bet League 1 campaign if the former Sheffield Wednesday man can stay fit.
He told the club’s official website: “As I’ve stated previously, I see Reda as a crucial part of our plans going forward.
“He stands out at this level in central defence and at the end of last season, our defensive performances were much improved with him in the side.
“It is no secret that we’d like to see him make more appearances during a season but with the help of physiotherapy department, I’m sure we can manage him in a way to help him do that.
“Also, he carries a significant goal threat from set-pieces and if we’re going to succeed, we need goals from all around the pitch next season.”