After his father's death in 864, an uprising was launched by a powerful Croatian nobleman from Knin called Domagoj.
Zdeslav overthrew him in 878 with the help of the Byzantines, expelled Domagoj's sons and restored peace with Venice.
[5] He most probably acknowledged the supreme rule of Byzantine Emperor Basil I, and Dalmatia (theme) influence expanded further into land, but not much.
[5] In 879, Pope John VIII asked Duke Zdeslav for an armed escort and protection for his legate who was crossing Croatia on his way to Bulgaria, ruled by Boris I.
[5] In early May 879, Zdeslav was killed by arrows near Knin in an uprising led by Branimir, a relative from Domagoj, possibly instigated by Pope John VIII fearing Byzantine power.