Original: Popes with the longest reigns The 10 longest-reigning popes whose reign lengths can be determined from contemporary historical data are the following: Pius IX (1846 1878): 31 years, 7 months and 23 days (11,560 days).
Simplified: Popes with the longest reigns The 10 longest-reigning popes : Pius IX (1846 1878): 31 years, 7 months and 23 days (11,560 days).