His parents were Pierre de Haerne (1780-1849), a lace merchant and minor government official, and Sophie-Catherine van der Ghote.

His brother Auguste de Haerne (1806-1870) became the "Doyen of Ninove", probably at the abbey of St. Cornelius, where he had a dozen priests under his direction; and another brother Louis de Haerne (1817-1887) became the king’s district commissioner of Eeklo (Echlo), and at times was administrator of the districts of Turnhout, Tielt and Roeselare (Roulers).

When he wrote against the Dutch King William I, he was forced in 1830 to flee Belgium, disguised as a horse merchant, and take refuge in France.

He returned the following year when Belgium gained independence from the Netherlands, and was elected in 1830, at the age of just 26, as the representative of Roeselare to the congress that helped to frame the Belgian constitution.

He also received in 1855 the honorary title of Canon of the Cathedral of Bruges, and Pope Pius IX in 1870 made him a bishop.