Under Emperor Henry III, he was a member of the court chaplaincy (Hofkapelle) in 1051/52, initially as the provost of St. Simon and Jude in Goslar and then in 1053 as Chancellor of Italy.
Hezilo was concerned to maintain the position of Hildesheim in and around Goslar, the heart of the Salian royal estate, where he and other leading members of the episcopate (including Adalbert of Bremen and Anno of Cologne) could exploit the situation whilst Henry IV was still a minor.
During the Saxon Rebellion and Investiture Controversy Hezilo played a part, sometimes vacillating, sometimes mediating.
Whilst Bishop of Hildesheim, Hezilo emerged as one of the great builders and patrons of the arts.
Emperor Henry IV granted forest rights (Forstbann) at Coppenbrügge to Bishop Hezilo of Hildesheim in 1062.