Slade served as manager of the Bluebirds for two years before being reassigned as the Championship side's 'head of football' last month.
In a statement, the club said: "Cardiff City FC can confirm that, by mutual agreement, Russell Slade has left his position as the club's Head of Football with immediate effect.
"We'd like to express our sincere thanks to Russell for his efforts in helping to move the club forward since arriving in 2014. He leaves with our very best wishes for the future."
Slade's departure comes amid rumours linking him to the top job at Charlton Athletic, who were relegated to League One at the end of last season.
In his two seasons in the Welsh capital, Slade led Cardiff to 11th and eighth-place finishes in the Championship.