During the 1995 Québec referendum campaign, Dion was a frequent television commentator, one of the few Québec intellectuals who defended the federalist position. His logical and precise attacks on the separatists caught the eye of Prime Minister Jean CHRÉTIEN, who asked the young professor to join his Cabinet.

Dion convinced the Cabinet to ask the SUPREME COURT whether a province could unilaterally secede from Canada. The court ruled on the secession case in August 1998, stating that a province could not, under international or domestic law, unilaterally declare sovereignty.