Longest time without a pope since AD33

The longest period of time during which the Catholic Church did not have a pope was from November 1268 to September 1, 1271, almost 3 years. This period is known as the interregnum (between reigns). The reasons were mostly political. It would have taken even longer, but the cardinals were locked in the Palazzo dei Papi di Viterbo to vote. They were given only bread and water and even the roof was removed making conditions very uncomfortable.

Eventually, Pope Gregory X was elected.