[1] He was born in the town of Allumiere, in the Province of Lazio, then part of the Papal States, the son of Isidore Mertel, a baker from Bavaria.

Among his posts was that of Prefect of the Congregation of St. Ives, a society of lawyers and procurators, providing pro bono defense of the poor in the courts.

Two months later, on 16 May, Pope Pius ordained him a deacon, so that at the moment when he was created cardinal he in fact was still not in holy orders - the last non-priest in history to be elevated to the cardinalate.

One result of this was that he attended Mass presided by his secretary Pietro Gasparri, who himself later became a Cardinal best known for his role in securing the Lateran Treaty with the Kingdom of Italy.

[3] Because Cardinal Mertel was not an ordained priest, the cardinal-priest title of San Lorenzo in Damaso was treated as a deaconry pro illa vice.