Adrian III was elected on May 17, 884, immediately after the death of Marinus I. His fifteen-month pontificate was devoted to the continuing Roman political crisis following the assassination of John VIII, and to the diplomatic management of the rapidly-disintegrating Carolingian empire under the ineffective Emperor Charles the Fat (882–887).
In summer 885, summoned by Charles the Fat to attend the Diet of Worms — convened to address the accelerating Carolingian succession crisis — Adrian III set out from Rome with the papal entourage on the journey north across the Alps.
He fell ill at San Cesario sul Panaro near Modena and died there on either September 8 or September 17, 885 — having travelled only as far as the Po valley. The monks of the nearby Abbey of Nonantola (founded 752 by St. Anselm of Nonantola) received the papal body for burial.
Adrian III is the only pope of the early-medieval period to be buried outside Rome — his tomb at the Abbey of Nonantola becoming the pilgrim destination of Emilia-Romagna and the object of immemorial local cult that would be formally confirmed by Pope Leo XIII's canonization decree of 1891.

