As a stockbroker he possessed ample capital with which to buy the work of artists with whom he was personally acquainted, including Eugène Delacroix and Alexandre-Gabriel Decamps.

He first expanded his family's collection to include paintings by Jean-Baptiste-Camille Corot, Narcisse Virgilio Díaz de la Peña, Constant Troyon, Théodore Géricault, Thomas Couture, Honoré Daumier and Charles-François Daubigny.

Moreau-Nélaton also belonged to the group of subscribers who secured and purchased Manet's Olympia for the nation of France in 1890.

His collection of impressionist painting was especially impressive, with 10 works by Claude Monet alone, including the well-known Poppyfield at Argenteuil.

Other painters represented in the collection included Pierre Puvis de Chavannes, Pierre-Paul Prud'hon, Johan Barthold Jongkind, Jean-Louis Forain and Eugène Carrière.