Hired on February 14, 2012, to be the team's special teams coaching assistant, Glenn moved to new roles in 2014 as quality control/defense coach, defensive assistant in 2016, assistant linebackers coach in 2017, and now leading the linebackers, being promoted before the 2018 season.

Hired on February 14, 2012, to be the team's special teams coaching assistant, Glenn moved to new roles in 2014 as quality control/defense coach, defensive assistant in 2016, assistant linebackers coach in 2017, and now leading the linebackers, being promoted before the 2018 season.

Last season, Glenn helped LB Jordyn Brooks transition from weakside linebacker to middle linebacker. Brooks led the NFC and was fifth in the NFL with 161 tackles, despite missing the final game due to injury (knee). It is also the fourth-most for a single-season in Seattle history. Cody Barton took over a starting role for the first time and recorded 136 tackles, four tackles for loss, a pair of sacks, six passes defensed and two interceptions. 

In 2021, Glenn led a linebacker room that saw Jordyn Brooks have a breakout campaign, ranking second in the NFL with a franchise-record 183 tackles. LB Bobby Wagner finished with 170 tackles, second most in franchise history, while being selected to his eighth consecutive Pro Bowl, tying Cortez Kennedy for third most in franchise history. Wagner was also named second-team All-Pro by the Associated Press, the only player in franchise history with eight All-Pro nominations.

In 2020, Wagner became the first player in franchise history to record nine-consecutive 100-tackle seasons. Wagner was voted to the Pro Bowl for the seventh time and selected to the Associated Press All-Pro first team. It was Wagner's fifth year in a row and sixth time in his career being named to the first-team (second-team in 2015; seven total), adding to a total that was already the most in franchise history.

In 2019, Glenn's linebackers saw career years, as Wagner recorded the second-most tackles in franchise history with 159 (1st in NFL), trailing his own franchise record of 167, and K.J. Wright posted a career-high 132 tackles, the fifth 100-tackle season of his career.

He entered the league after spending two seasons (2010-11) as the University of Washington's quality control coach.

Glenn was a three-year letterwinner at linebacker and a starter on East Stroudsburg University's 2004 and 2005 NCAA playoff teams. He was also a two-year letterwinner in basketball in 2001-02 and 2002-03.

Born on July 20, 1981 in Scranton, Pa., Glenn and his wife, Leigh, have three sons, Nate, Luke, and Will.