His depictions of scenes from the life of the disadvantaged and lower-class people of his time mark him as the first Belgian social realist painter.
This work depicting a dying woman, her drunk husband and their young children in a cramped and poorly lit room signaled a clear break with the lofty and elegant style and subjects of his master Navez.
[6] He was also invited to provide designs for the stained glass windows of the Cathedral of St. Michael and St. Gudula, which were executed by Jean-Baptiste Capronnier.
It depicts a woman who is lying sick and dying on her bed while her drunk husband holding a bottle is brought in by two young children.
The sober palette and the execution that neglected detailed depiction for global effect as well as the subject matter were de Groux' radical break with the Classicist style of Navez in favor of the 17th century genre painters such as Adriaen Brouwer.
During this period de Groux painted many compositions depicting the disadvantaged people of his day in their misery and vices such as alcoholism and lassitude.
He still painted some history scenes in this later phase such as The death of emperor Charles V (Royal Museums of Fine Arts of Belgium) and Frans Junius preaching the Reformation in secret in Antwerp.
[12] De Groux influenced many young, realistic painters, including his pupil Constantin Meunier and Eugene Laermans.
Even the later society painter Gustave Léonard de Jonghe painted early in his career a social realist painting called Pilgrims Praying to Our Lady of the Afflicted or Our Lady of Mercy (1854, Royal Museums of Fine Arts of Belgium), which was clearly influenced by de Groux' social realist works.