Diez was born at Giessen, in Hessen-Darmstadt. He was educated first at the gymnasium and then at the university of his native town and Göttingen. There he studied classics under Friedrich Gottlieb Welcker who had just returned from a two years' residence in Italy to fill the chair of archaeology and Greek literature. It was Welcker who kindled in him a love of Italian poetry, and thus gave the first outlet to his genius. In 1813 he joined the Hesse corps as a volunteer and served in the French campaign. Next year he returned to his books, and this short taste of military service was the only break in a long and uneventful life of literary labours.