Hartwig (died 866) was the tenth Bishop of Passau from 840 to 866.
Hartwig was the head of the Königskloster Tegernsee, and perhaps a member of the Hofkapelle and a family member of King Ludwig of Germany.
In 862 or 863 he suffered a serious stroke, and spent his remaining years largely disabled. In 866, he was succeeded by Ermanrich as new Bishop of Passau.