"This donation, exceptional both in its size and its consistency, is the biggest received by a French museum from a French museum since 1945," the French culture ministry said on Friday.
The 89-year-old couple have bequeathed their huge collection to Paris's Seineside museum of 19th-century art when they die but 187 works, worth 173 million euros, were to be donated on Saturday.
Degas, Corot and les Nabis
The collection includes works by well-known artists like Edgar Degas, Odilon Redon, Gustave Caillebotte, Camille Corot and Amedeo Modigliani but the couple are most interested in the works of the Nabis, a group named after the Hebrew word for prophet who aimed to revitalise painting, and its members are well-represented with 23 works of Edouard Vuillard, 12 by Pierre Bonnard and four by Maurice Denis.
Their enthusiasm is shared by Musée d'Orsay president Guy Cogeval, who has known the couple since 2001.
A condition for the donation was that the collection be kept together and it will be exhibited in a 900m² room that has been set aside.
Spencer Hays made his money in various fields, starting as a door-to-door book salesman in Nashville, Tennessee.
The couple have an apartment in New York, decorated with many of their works, and have built a copy of a Paris mansion in Nashville.