Born in Eugene, Oregon, Wilcox grew up as the younger of two sons on a family farm (wheat and cherries) in nearby Junction City.

He graduated in 1995 and considered Stanford and Arizona but followed family tradition and accepted a scholarship to Oregon under head coach Mike Bellotti.

[3] After redshirting his first year at Oregon, Wilcox found himself buried on the depth chart and switched to defensive back.

[4] After three seasons at Cal, Wilcox returned to Boise State in 2006 as the defensive coordinator under new head coach Chris Petersen.

[6] Following the 2009 season, Wilcox accepted the defensive coordinator job at Tennessee under new head coach Derek Dooley.

[8] Early on January 2, 2012, reports emerged that Wilcox was to become the new defensive coordinator at Washington in Seattle, under head coach Steve Sarkisian.

The position was vacant due to Nick Holt's termination days earlier,[9] and the announcement was made official later that night.

[15] The Bears went 5–7 during Wilcox's first year in 2017, with wins over North Carolina, Ole Miss, and #8 Washington State, and three losses by three points or fewer.

The Bears upset #15 2018 Washington 12–10 and defeated USC 15–14 at the Coliseum in Los Angeles to snap a 14-year losing streak to the Trojans.

In contrast to his predecessor, Sonny Dykes, Wilcox emphasized a strong defense, cutting Cal's points allowed per game from 42.6 (2016) to 20.4 (2018).

Justin's brother, Josh Wilcox, was three years ahead in school and played tight end for the Ducks and two seasons in the NFL with the New Orleans Saints.