Currently the Sydney Roosters' SG Ball coach, Cordner reunites with head coach Laurie Daley, who appointed him to the Blues captaincy in 2017 during his first stint as coach.
Cordner will serve as defensive coach as the Blues fight to recover from a disappointing 2025, when they lost a decider at home after leading the series 1-0.
The 33-year-old served as a trainer for the past two series and was previously an assistant coach at the Roosters under Trent Robinson.
His appointment comes after Young stepped down to replace the departing Shane Flanagan as Dragons coach for the remainder of 2026.
"It is such a great honour and I am so excited about the opportunity to step into the role," Cordner said of his appointment.
"I will put everything I've got into it. I have been in and around it learning off the coaches and I've been a player in this arena, so I understand what it takes."
Cordner is considered one of the Blues' modern greats, making 16 appearances for his state and captaining the side to series wins in 2018 and 2019.
His final game of professional rugby league came in the 2020 post-season series, when he suffered the last in a string of concussions in the opening match.
Cordner brings premiership experience to the coaching role, having played in the Roosters' 2013, 2018 and 2019 NRL grand-final wins.
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