His father, whose name he shared, was a successful psychiatrist who ran a fashionable clinic on the heights of Montmartre, and he was brought up in the rich Parisian neighborhood of Passy in a house that had belonged to the Princesse de Lamballe.
His father's drawing room was frequented by many of the Parisian celebrities in literature and the arts — including Jules Michelet, Charles Renouvier, Hector Berlioz, Camille Corot, Louis Français, and numerous others.
At Dr. Blanche's house there were regular Saturday meetings devoted either to some artistic performance or to conversation about aesthetic or literary subjects.
[7] Among the painter's most famous works are portraits of his father, Marcel Proust (private collection, Paris), the poet Pierre Louÿs, the Thaulow family (Musée d'Orsay, Paris), Aubrey Beardsley (National Portrait Gallery, London), and Yvette Guilbert and the infamous beauty Virginia Oldoini, Countess of Castiglione whom his father had treated for mental illness.
Others he painted included James Joyce, Julia Stephen, Edgar Degas, Claude Debussy, Auguste Rodin, Colette, Thomas Hardy, John Singer Sargent, Charles Conder, Percy Grainger, and Tamara Karsavina as Stravinsky's Firebird.
[9] One of his lovers may have been the Spanish painter Rafael de Ochoa, whom Blanche wrote shared the "same tendencies",[10] and features with him in a self-portrait.