Indy took the 6-foot-7, 311-pound tackle with the 22nd overall pick.
He is expected to solidify an offensive line that has not produced a 1,000-yard runner the last two seasons, allowed defenders to take too many shots at Peyton Manning and has been aging. Colts vice chairman Bill Polian criticized the line for the Super Bowl loss two years ago because of the inability to convert on short yardage situations.
Castonzo is considered a good pass protector with a quick first step and a solid drive blocker.
He could fill the void created when former second-round pick Tony Ugoh was released last season.