The 50-year-old, who played 408 matches for Forest during two spells totalling nearly 12 years, has taken up a role with the Rams as a defensive coach.
His son Tyler, a 19-year-old striker, also now plays for Forest, while 17-year-old son Lewis represents the Rams.
Academy director Darren Wassall, who played with Walker at Forest, said the ex-England man had "plenty to offer".
Walker won 59 caps during his career and played for England at the 1990 World Cup, when they reached the semi-finals, and Euro 92.
Former Derby defender Craig Short has also joined the academy coaching set-up.
Nottingham Forest legend Des Walker has joined fierce rivals Derby County as an academy coach.