Justus de Harduwijn, also written Hardwijn, Herdewijn, Harduyn or Harduijn (11 April 1582 – 21 June 1636 in Oudegem), was a 17th-century Roman Catholic priest and poet from the Southern Netherlands.
His father was a friend of writer Jan van der Noot who had introduced him to the French poets of La Pléiade, and is said to have been the first translator of Anacreon into Dutch.
The same year the biblical poetry of Den val en de Opstand van David/Leed-tuyghende Pasalmen (David's fall and rise / Penitential Psalms) was published as well.
In 1635 de Harduwijn, together with David Lindanus, wrote Goeden Yever tot het Vaderland ter blijde inkomste van den Coninclijcken Prince Ferdinand van Oostenryck (Good Zeal for the Fatherland on the joyous entry of the Royal Prince Ferdinance of Austria), celebrating the Joyous Entry of Cardinal-Infante Ferdinand of Austria as Governor General of the Spanish Netherlands.
During the 20th century, Oscar Dambre, a literary historian from Ghent, devoted several studies to de Harduwijn, and composer Arthur Meulemans put his text Clachte van Maria benevens het Kruis (Mary's lament by the cross) to music.