Born in Dinant from a relatively poor family, he entered the Antwerp art academy in 1820.
During his stay in Rome, Wiertz worked on his first great work, Les Grecs et les Troyens se disputant le corps de Patrocle ("Greeks and Trojans fighting for the body of Patroclus", finished in 1836), on a subject borrowed from book XVII of Homer's Iliad.