Stephen V was elected on September 17, 885, after the death of Adrian III in Italy. His six-year pontificate was devoted to the management of the accelerating disintegration of the Carolingian empire — Emperor Charles the Fat was deposed in 887, and the empire fragmented into competing successor kingdoms.
Stephen V crowned the Italian king Guy III of Spoleto as emperor in 891 — the first non-Carolingian emperor since the Carolingian foundation of the imperial title in 800. The coronation marks the definitive end of the Carolingian-imperial period and the beginning of the post-Carolingian Italian-imperial-papal politics that would culminate in the Saxon-Ottonian renewal of 962.
His most consequential — and regrettable — act was the 885 papal letter to the Slavic prince Svatopluk of Greater Moravia suppressing the Slavonic liturgical tradition of the Cyrillo-Methodian mission. After the death of St. Methodius (April 6, 885), Stephen V yielded to the pressure of the Frankish episcopate (especially Wiching of Nitra) and reversed the Adrian II / John VIII Slavonic-liturgy approvals — banning the Slavonic-language liturgy and expelling the Methodian disciples from Moravia.
The expelled Methodian disciples (Clement of Ohrid, Naum of Preslav, etc.) took refuge in the Bulgarian kingdom of Boris I, where the Slavonic liturgical and biblical translation tradition continued and produced the Bulgarian-Slavonic Catholic-Orthodox culture that would evangelize the rest of the Slavic world (Serbia, Russia). The Stephen V suppression in Moravia thus produced the geographical-eastward redirection of the Slavonic Christian tradition.
Stephen V died on September 14, 891.