Joseph Chaumet (1852–1928) was the jeweller who gave the house founded by Marie-Étienne Nitot in 1780 its lasting name. He worked with the jeweller Prosper Morel, whose firm descended from Nitot through Jean-Baptiste Fossin, and married Morel's daughter Marie (Blanche-Marie), taking over the direction of the house in 1885; it has carried the name Chaumet ever since.
A visionary of the Belle Époque, he made tiaras and aigrettes, lighter alternatives to the diadem, into signatures of the house, turning these emblems of rank into instruments of style. He kept the Renaissance manner for tiaras, then very much in vogue, while drawing on Japanese art, the pointed arches of Islamic architecture and Art Nouveau nature motifs, producing bat-shaped aigrettes, carved combs and naturalistic jewels of flowers and foliage. His clients included Indian maharajas, the Russian imperial family and European collectors.
He was also a technician. He set up a laboratory to identify gemstones, and between 1904 and 1914 filed about ten patents that advanced the science of gemmology. In 1907 he moved the workshops and boutique to 12 place Vendôme, the Hôtel Baudard de Sainte-James, which remains the house's home, with its boutique, historic salons and high jewellery workshop, and installed a photographic studio there to record every piece that left the workshops. The house took part in the 1925 Exposition internationale des arts décoratifs in Paris. He was succeeded in 1928 by his son Marcel.
Sources differ on the marriage: English Wikipedia dates it to 1885, when he took control, while French Wikipedia says he married Blanche-Marie Morel in 1875 and took over in 1885.