"I've got another person who lives in my house that is extremely important to me, and we just decided now is the time," said Johnson.
Johnson said he and his wife would eventually move to South Carolina, where they both have family.
Nashville sports radio station 104.5 the Zone reported earlier in the day that Johnson would resign after eight seasons with the Commodores. Johnson clarified that he was retiring - not resigning.
Assistant head coach Robbie Caldwell was named interim head coach until a replacement could be found. Caldwell has coached with Johnson at Vanderbilt since 2001.
Johnson has a 29-66 record with Vanderbilt and an 89-102 career record. He took the 'Dores to the Music City Bowl with a 7-6 record in 2008, but struggled during the 2009 season. The team went 2-10, going winless in the Southeastern Conference, and losing the last eight games of the season.
Bobby Johnson Retires As Vanderbilt Head Football CoachMore>>