1650s, "unroll, unfold" (a sense now obsolete), from French développer. It replaced earlier English disvelop (1590s, from Middle French desveloper); both French words are from Old French desveloper "unwrap, unfurl, unveil; reveal the meaning of, explain," from des- "undo" (see dis-) + veloper "wrap up," which is of uncertain origin, possibly Celtic or Germanic.
The modern uses are figurative and emerged in English 18c. and after: Transitive meaning "unfold more fully, bring out the potential in" is by 1750; intransitive sense of "come gradually into existence or operation" is by 1793; that of "advance from one stage to another toward a finished state" is by 1843. The intransitive meaning "become known, come to light" is by 1864, American English.
The photographic sense "induce the chemical changes necessary to cause a latent picture or image to become visible" is from 1845; the real estate sense of "convert land to practical or profitable use" is by 1865. Related: Developed; developing. Developing as an adjective in reference to poor or primitive countries or nations that are advancing in economic, industrial, and social conditions is by 1960.