The Bucs also announced Mark Dominik was hired as general manager, succeeding Bruce Allen.
The announcement came a day after Gruden and Allen were let go.
Morris, who is 32, started last season as defensive backs coach and was elevated to defensive coordinator when Monte Kiffin left the team for a position at the University of Tennessee.
"In anything with change, you have questions, but I think the one thing that Coach Morris will bring to the table is energy, everybody being on the same page at the same time, from top to bottom," Pro Bowl linebacker Derrick Brooks said.
Dominik has been the team's pro personnel director since 2001.
Gruden joined the Bucs in 2002 and led them to the Super Bowl championship that season. This year's Tampa Bay team lost its last four games, finished 9-7 and missed the playoffs.