Dell'Olio studied at the seminary in Bisceglie and then at the Pontifical University of Saint Thomas Aquinas in Rome where his professors included the future cardinal Tommaso Maria Zigliara. In 1873 he received the rank of Doctor of Theology.
Dell'Olio was ordained as a priest on 23 December 1871. In 1876 he became professor of philosophy and theology at the seminary in Bisceglie. In 1882 he founded the institute "Giovanni Bosco".
On 14 December 1891, Dell'Olio was elected archbishop of Rossano and on 20 December of the same year he was consecrated as bishop in Rome by cardinal Raffaele Monaco La Valletta.
On 5 February 1898 Dell'Olio was promoted to Archbishop of Benevento. The diocese welcomed him on 29 May 1898. In that city he founded the Ateneo Pontificio in 1899.
In Dell'Olio's speech at the inauguration of the institution, the cardinal said:
I have sought from the beginning, an idea, almost a dream, a dream of those who love good and cannot reach it: But now, gentlemen, that which in the beginning seemed a dream, thanks to the beneficence of Leo XIII, whom the people of Benevento hold in the utmost esteem with every thought... is a solemn reality, and is before our eyes (and you are such a great part of it), that is, the Theological-Juridicial Institute in the augmented form of a Pontifical University.
The day has come, in which you gentlemen chosen to hold the professorial chairs and you dear young boys embarking on noble studies will enter the palaistra prepared for you, the one group to spread the doctrines of the science of divinity, the other to attain them
Pope Leo XIII raised Dell'Olio to the rank of cardinal in the Papal consistory of 15 April 1901 and he received the titular church of Santa Balbina.
On 16 June 1901 Dell'Olio was in Benevento to consecrate the Basilica della Madonna delle Grazie and its altar which was "a splendid gift from the munificence of Leo XIII."
Dell'Olio died at Benevento at the age of 54 and his body was buried in the city of Benevento in the old cemetery of Santa Clementina.
