Reynolds, 35, replaces Dan Quinn, who was fired by new head coach Cam Cameron last week, reportedly after he declined to sign a contract extension. Reynolds was on Cameron's college staff at Indiana in 2001.
Quinn earlier this week was hired by the New York Jets as their defensive line coach and signed a two-year contract.
It marks the second consecutive day on which Colts coach Tony Dungy has lost an assistant from his Super Bowl XLI champion staff. On Thursday, defensive backs coach Leslie Frazier was hired by the Minnesota Vikings as their new defensive coordinator.
The top priority for Reynolds will be to develop some of Miami's younger defensive linemen. The Dolphins have seven defensive linemen who will be at least 30 before the start of the 2007 season. That includes two players, tackles Keith Traylor and Jeff Zgonina, who are older than Reynolds.
There were rumors last week, before the Super Bowl, that Reynolds was in line for the job on the Dolphins' staff.
Reynolds has been on the Indianapolis staff since 2002, when Dungy hired him. A college linebacker at Wake Forest (1989-93), he began his coaching career at his alma mater in 1997. He moved to Indiana in 2001 and then to the Colts the following year.
Miami also officially announced the hiring of Matt Schiotz, who will serve as the primary strength and conditioning coach. There already had been various reports that Schiotz, 36, had agreed to join Cameron's staff.
Schiotz was the assistant strength coach with the San Diego Chargers for the past five seasons.
Len Pasquarelli is a senior NFL writer for ESPN.com.