Hartmut von St. Gallen (died 23 January after 905 in Saint Gall) was abbot of the Abbey of Saint Gall.

Hartmut (Old High German "of powerful courage and spirit"), was monk, pupil of Rabanus Maurus at the Princely Abbey of Fulda, and became Grimald's successor as Abbot of Saint Gall in 872. Otfrid of Weissenburg dedicated his Old High German "Liber evangeliorum", a kind of diatessaron in southern Rhenisch Franconian dialect, i. a. to his friend and fellow student Hartmut. As abbot, Hartmut, like his predecessor, generated an abundant construction activity. In 883, he abdicated and afterwards led a life of seclusion as recluse near the monastery in Saint Gall. He died on a 23 January after 905.