Rogier descended from a family settled in the department of the Nord in France. He was born in Saint-Quentin. His father, an officer in the French army, perished in the Russian Campaign of 1812. The family then moved to the Belgian city of Liège, where the eldest son, Firmin, held a professorship. Rogier studied law at the University of Liège (ULg) and was admitted to the Bar. However, he devoted himself with greater zeal to journalistic campaigns against the Dutch rule in Belgium, established by the Congress of Vienna in 1815. In 1824, in collaboration with his lifelong friends Paul Devaux and Joseph Lebeau, he founded the journal "Mathieu Laensberg" (afterwards "Le Politique"). With its ardent patriotism and its attacks on the Dutch administration, the journal soon achieved widespread influence.