On 14 November 1889 Demarçay married Jeanne Berard (1865–1933) at the Temple du St. Esprit, Paris, in a  Protestant wedding. His granddaughter, Joseph de Carayon Talpayrac, was alive in Paris in 2003.
Eugène-Anatole Demarçay died 5 March 1903, at his home at 80 Boulevard Malesherbes, Paris. His brother Jean became executor of his estate, and offered the state of the art equipment from his laboratory to Pierre Curie. Curie eventually arranged for it to be given to rare earths researcher Georges Urbain.