Glasgow, 38, was a member of Gary Patterson's original staff and has coached one of the nation's best pass defenses.
Tech also promoted Otis Mounds, 39, from graduate assistant to assistant coach in charge of cornerbacks.
"It's my goal to bring our defense to a championship level and Chad Glasgow is the right person for the job," Texas Tech coach Tommy Tuberville said in a statement. "With his experience and knowledge of the game and recruiting, he will be a great addition to our staff."
Glasgow replaces James Willis, who was at Tech for one season before leaving the program in late December.