Gérard Paul Deshayes (May 13, 1795 – June 9, 1875) was a French geologist and conchologist.

He was born in Nancy, his father at that time being professor of experimental physics in the École Centrale of the Meurthe département.

He studied medicine in Strasbourg, and afterwards took the degree of bachelier ès lettres in Paris in 1821; but he abandoned the medical profession in order to devote himself to natural history. For some time he gave private lessons on geology, and subsequently became professor of natural history in the Museum d'Histoire Naturelle.

He was distinguished for his researches on the fossil mollusca of the Paris Basin and of other Tertiary areas. His studies on the relations of the fossil to the recent species led him as early as 1829 to conclusions somewhat similar to those arrived at by Lyell, to whom Deshayes rendered much assistance in connection with the classification of the Tertiary system into Eocene, Miocene and Pliocene.

He was one of the founders of the Société Géologique de France. In 1839 he began the publication of his Traité élémentaire de conchyliologie, the last part of which was not issued until 1858. In the same year (1839) he went to Algeria for the French Government, and spent three years in explorations in that country. His principal work, which resulted from the collections he made, Mollusques de l'Algérie, was issued (incomplete) in 1848.

In 1870 the Wollaston medal of the Geological Society of London was awarded to him. He died in Boran - sur - Oise.