<P> Pope Pius IX ( Italian : Pio ; 13 May 1792 -- 7 February 1878 ) , born Giovanni Maria Mastai - Ferretti , was head of the Catholic Church from 16 June 1846 to his death on 7 February 1878 . He was the longest - reigning elected pope in the history of the Catholic Church , serving for over 31 years . During his pontificate , Pius IX convened the First Vatican Council ( 1869 -- 70 ) , which decreed papal infallibility , but the council was cut short owing to the loss of the Papal States . </P>
<P> Pope Pius IX ( Italian : Pio ; 13 May 1792 -- 7 February 1878 ) , born Giovanni Maria Mastai - Ferretti , was head of the Catholic Church from 16 June 1846 to his death on 7 February 1878 . He was the longest - reigning elected pope in the history of the Catholic Church , serving for over 31 years . During his pontificate , Pius IX convened the First Vatican Council ( 1869 -- 70 ) , which decreed papal infallibility , but the council was cut short owing to the loss of the Papal States . </P>
who was the longest reigning pope in church history
who was the longest reigning pope in church history
Pope Pius IX
Pope Pius IX