Wiertz was born in Schaesberg, Limburg, and he went to the Maastricht Academy of Music.

He has also studied at the Utrecht and Leiden Universities, and he became a music teacher at the Rotterdam Sint-Laurenscollege high school in 1982.

Wiertz worked as a composer and arranger for public broadcasters VARA, KRO, and NOS as well as for the musicals Kaat Mossel (1992) and Mooi Katendrecht (1994) in Rotterdam.

[1] He became principal of Sint-Laurenscollege in 2006, and he filled the same position simultaneously at Eckartcollege and Pleincollege – located in Eindhoven and Nuenen, respectively – between 2011 and 2017.

[2] Wiertz declared he wanted to restore the party's stability, honesty, and reliability following a loss of seats in the November 2023 general election.