Champagné was born into a family of French Huguenot exiles in Ireland, the son of the Very Rev. Arthur de Robillard Champagné, Dean of Clonmacnoise, and Marianne Hamon, daughter of Colonel Isaac Hamon. His paternal great-grandfather was Chevalier Josias de Robillard, Seigneur de Champagné de Torxé, Saintonge, who fled to Holland after the Edict of Fontainebleau in 1685, joining William of Orange's army. He married Marie de la Rochefoucauld of the noble house of the same name. Their daughter Susanne married Henri de la Motte-Fouqué, baron de Saint-Seurin et de Tonnay-Boutonne, and was mother of Heinrich August de la Motte Fouqué. Their eldest son, Josias de Robillard (Forbes' grandfather), distinguished himself at a young age in service of Major-General Isaac de Monceau de la Melonière, who commanded a regiment of exiles in William's army during the Irish campaigns. He married Lady Jane Forbes, daughter of Arthur Forbes, 2nd Earl of Granard.