[1] Born in Kerkrade as the oldest in a family of nine, Wiertz studied at the Minor seminary Rolduc, from where he graduated in 1961, having passed his state examinations.

He received his episcopal consecration on September 25 of that year, from Adrianus Johannes Cardinal Simonis, archbishop of Utrecht, with the bishop of 's-Hertogenbosch, Joannes Gerardus ter Schure, and the auxiliary bishop of Roermond, Alphonsus Maria Henricus Antonius Castermans, serving as co-consecrators.

He chose the motto Geef, Heer, liefde en geloof aan uw Kerk (English: Give, Lord, love and faith to your Church).

On 8 December 2018 Harrie Smeets, dean of the deanery of Venray and a member of the cathedral chapter, was appointed bishop of Roermond.

[9] After his retirement Wiertz settled in Maastricht and remains part of the administration of the diocese of Roermond as bishop emeritus.