PARIS — When French President Emmanuel Macron needed someone to lay out the options for reforming French aid, he landed on Hervé Berville, a Rwandan-born economist and freshman politician in France’s national assembly. 

The 28-year-old was adopted by a French couple after being evacuated from an orphanage in Kigali, Rwanda, by the French army during the 1994 genocide. Brought up in Brittany, and educated in Lille and the London School of Economics, he worked for two years with the French aid agency Agence Française du Développement in Mozambique ...