He is listed as a member of the ANS since May 21, 1878. During his early years at New York De Morgan quickly became acquainted with the American numismatic community and early in 1878 was actively selling. Consequently, he was a frequent traveler the remainder of his life. In 1878 he moved to New York on Lafayette Place, traveling back and forth abroad to various excavations over the next thirty-one years. In 1872, a teenager of eighteen, he and his younger brother became associated with French archaeologists : Abbot Cochet, Alexandre Bertrand, Louis Laurent Gabriel de Mortillet (1821-1898) a noted archaeologist and anthropologist specializing in Paleolithic man, at the Neolithic excavation site Le Campigny near Rouen, where they discovered prehistoric pottery. He and his younger brother Jacques were students of antiquities at l'Ecole des mines de Paris, studying mining engineering in the footsteps of their father.

Henri de Morgan (1854-1909), was born at Huisseau, sur, Cossonay, Cher, Centre, France, son of Eugène de Morgan (1829-) and Louise Marie Caroline Henrietta de Calonne d'Avesnes de Morgan (1832-1864). He is the elder brother of Jacques Jean-Marie de Morgan (1857-1924), Director of the Department of Antiquities in Egypt (1892-1897), also a very well-known archaeologist who discovered the Stele of Hammurabi now in the Louvre Museum, Paris, France. The objects he excavated and collected were divided between three disparate museum collections : the Brooklyn Museum, the Musée des Antiquités Nationales in Saint-Germain-en-Laye in Paris, and the Egyptian Museum in Cairo. In the winter months of 1906 through 1908 he directed excavations of prehistoric, i.e., predynastic sites in Upper Egypt between Esneh and Edfu for the Brooklyn Institute Museum. In New York he was an associate of Thomas Benedict Clarke (1848-1931). He was an expert in French medieval, Greek, Persian, and Egyptian antiquities. Henri de Morgan was an archaeologist, numismatist and coin dealer who also catalogued for several auctions in New York City where he kept a shop.

Henri by Ella Frank