Jean Calas was a French Huguenot who came under scrutiny when his son, Marc-Antoine Calas, was found dead in 1761. Authorities quickly suspected suicide, linking it to his father's alleged opposition to the son's conversion to Catholicism. The trial exhibited overt religious bias against Protestants, leading to a rapid conviction. Despite lacking substantial evidence, Calas was subjected to gruesome torture in an effort to extract a confession, which he maintained was false. The judicial process was heavily influenced by the prevailing anti-Huguenot sentiment of the time, revealing glaring injustices within the legal system.

As Calas languished in custody, public outrage grew, especially among the intellectual elite. Voltaire, a prominent philosopher and advocate for civil liberties, became aware of Calas's plight and the grotesque miscarriage of justice he faced. Moved by the case, Voltaire penned letters and essays calling for reform, emphasizing the necessity of compassion and rationality in law and religious tolerance. He saw Calas as a symbol of the suffering imposed by religious intolerance and began a broader campaign for legal reform in France, urging improvements to the justice system to prevent similar injustices.

The eventual posthumous exoneration of Jean Calas not only restored his family's honor but also served as a catalyst for wider discussions regarding human rights and legal reforms in France. Voltaire's involvement brought the case to international attention, leading to changes in public opinion and setting a precedent for future challenges against religious and legal oppression. The case encapsulated the conflicts between religious identity and civic rights in an era marked by enlightenment thought and burgeoning humanistic ideals.