For most of his pontificate, Zachary's more pressing concern than distant Frankish politics was the Lombard kingdom pressing on Rome's own doorstep from the north. The Lombard king Liutprand had already conquered large parts of the Byzantine exarchate of Ravenna and repeatedly threatened Rome itself, and rather than relying on Byzantine military help that rarely arrived in time or in force, Zachary chose direct personal diplomacy, traveling to meet Liutprand and negotiating with him face to face on more than one occasion.
The approach worked with real success. Zachary persuaded Liutprand to restore territory the Lombards had seized from the church, including the cities of Amelia, Orte, Bomarzo and Blera, and separately convinced him to hold back from finishing the conquest of Ravenna, preserving the exarchate for a further period. He achieved similar results with Liutprand's successor Rachis, whom Zachary is said to have persuaded to abandon a siege of Perugia and, according to later tradition, ultimately to abdicate and enter a monastery.
Zachary's Lombard diplomacy bought Rome roughly a decade without the destruction that would follow only a few years after his death, when a later Lombard king, Aistulf, broke the truce his predecessors had kept and seized Ravenna outright, provoking Pope Stephen II to call on the same Frankish king Zachary had helped make legitimate, Pepin the Short, for the military intervention that permanently reshaped papal territory into what became the Papal States.