Pope Pius IX ( May 13 , 1792 â `` February 7 , 1878 ) , born Giovanni Maria Mastai-Ferretti , reigned as Pope of the Roman Catholic Church from his election in June 16 , 1846 , until his death more than 31 years later in 1878 , making him the longest-reigning Pope since the Apostle , St. Peter . Blessed Pope Pius IX ( 13 May 1792 , Senigallia â `` 7 February 1878 ) , born Giovanni Maria Mastai-Ferretti , was the longest-reigning elected Pope in the history of the Catholic Church , serving from 16 June 1846 until his death , a period of nearly 32 years .