He made his first trip to North-eastern India in 1895. In 1922 he was asked by the governments of France and Afghanistan to organize an archeological co-operative which became the Délégation Archéologique Française en Afghanistan.
Foucher's most famous work was L'Art Greco-Buddhique du Gandhara (translated by L.A. Thomas and F.W. Thomas as The Beginnings of Buddhist Art), in which he described how Buddhist art prior to Pan-Hellenism was principally aniconic, representing the Buddha by depicting elements of the Buddha's life instead of depicting the Buddha himself. Foucher argued that the first sculpted images of the Buddha were heavily influenced by Greek artists.
Since then, Foucher's argument has been revised such that most now believe that the influence was Roman, as opposed to Greek. Nonetheless, his central thesis that the Buddha was of Classical origin has beome established.
For a compelling counter-argument to Foucher's essay, see Ananda K. Coomaraswamy, "The Origin of the Buddha Image."