Harrell, 29, joined Washington State's coaching staff in 2014 as an offensive analyst focusing on film breakdown and player evaluation. He replaces Dennis Simmons, who left for a similar job at Oklahoma last week.
Harrell finished his career at Texas Tech under Leach as the NCAA's all-time passing touchdowns leader (134). He also became the first quarterback to surpass 5,000 passing yards in back-to-back seasons. In 2008, his final year at Texas Tech, Harrell was the Johnny Unitas Golden Arm Award winner, the AT&T All-America Player of the Year and the fourth-place finisher in Heisman Trophy voting.
Harrell spent the 2009 season in the Canadian Football League before three with the Green Bay Packers. He appeared in four games, all in 2012, and won a Super Bowl with the team in 2010.
Washington State finished 3-9 last season, including 2-7 in Pac-12 play.
- Josh Sanchez