Glenn originally signed his letter of intent to play college football for the Purdue Boilermakers in 1990.
[8] In 1996, Glenn set the team record for longest interception return with a 100-yard touchdown against the Miami Dolphins.
He started 16 games at left cornerback, registering 75 tackles, 5 interceptions, 16 passes defensed and one sack.
He and teammate Gary Walker became the first Texans player to reach the NFL Pro Bowl in 2002.
In 2003, he started 11 games and was declared inactive in 2 because of injury, before being placed on the injured reserve list for the final 3 contests.
Glenn signed with the Dallas Cowboys before the 2005 season, reuniting him with Bill Parcells, who was his head coach with the New York Jets.
Coming in as a 33 year old free agent, he surprised observers with his high level of play.
Although he was projected to be involved only on the nickel defense, he started 7 games in place of an injured Anthony Henry and recorded 4 interceptions (led the team).
[18] On January 23, 2021, Glenn was hired by the Detroit Lions as their defensive coordinator under head coach Dan Campbell.