In 1921 Mitsou, a book which included forty drawings by Balthus, was published. It depicted the story of a young boy and his cat, with a preface by Balthus's mentor, Rilke. The theme of the story foreshadowed his life-long fascination with cats, which resurfaced with his self-portrait as The King of Cats (1935). In 1926, visited Florence, copying frescos by Piero della Francesca, which inspired another early ambitious work by the young painter: the tempera wall paintings of the Protestant church of the Swiss village of Beatenberg (1927). From 1930 to 1932 he lived in Morocco, was drafted into the Moroccan infantry in Kenitra and Fes, worked as a secretary, and sketched his painting La Caserne (1933).
Early on his work was admired by writers and fellow painters, especially by André Breton and Pablo Picasso. His circle of friends in Paris included the novelists Pierre Jean Jouve, Antoine de Saint-Exupéry, Joseph Breitbach, Pierre Leyris, Henri Michaux, Michel Leiris and René Char, the photographer Man Ray, the playwright and actor Antonin Artaud, and the painters André Derain, Joan Miró and Alberto Giacometti (one of the most faithful of his friends). In 1948, another friend, Albert Camus, asked him to design the sets and costumes for his play L'Etat de Siège (The State of Siege, directed by Jean-Louis Barrault). Balthus also designed the sets and costumes for Artaud's adaptation for Percy Bysshe Shelley's The Cenci (1935), Ugo Betti's Delitto all'isola delle capre (Crime on Goat-Island, 1953) and Barrault's adaptation of Julius Caesar (1959-1960).
In 1977 he moved to Rossinière, Switzerland. That he had a second, Japanese wife Setsuko Ideta whom he married in 1967 and was thirty-five years his junior, simply added to the air of mystery around him (he met her in Japan, during a diplomatic mission also initiated by Malraux). A son, Fumio, was born in 1968 but died two years later.
The photographers and friends Henri Cartier-Bresson and Martine Franck (Cartier-Bresson's wife), both portrayed the painter and his wife and their daughter Harumi (born 1973) in his Grand Chalet in Rossinière in 1999.
Prime Ministers and rock stars alike attended the funeral of Balthus. Bono, lead-singer of U2, sang for the hundreds of mourners at the funeral, including the President of France, the Prince Sadruddhin Aga Khan, supermodel Elle McPherson, and Cartier-Bresson.
Many of his paintings show young girls in an erotic context. Balthus insisted that his work was not erotic but that it recognized the discomforting facts of children's sexuality.
His favourite composer was Wolfgang Amadeus Mozart.
According to most biographies, Balthus denied having any ethnic Jewish heritage, claiming that biographers had confused his mother's true ancestry. In Balthus: A Biography, Nicholas Fox Weber, who is Jewish, attempts to find common ground while interviewing the painter by bringing up a biographical note stating that his mother was Jewish. Balthus replied, "No, sir, that is incorrect," and explained: "One of my father's best friends was a painter called Eugen Spiro, who was the son of a cantor. My mother was also called Spiro, but came apparently from a Protestant family in the south of France. One of the Midi Spiros - one of the ancestors - went to Russia. They were likely of Greek origin. We called Eugen Spiro "Uncle" because of the close relationship, but he was not my real uncle. The Protestant Spiros are still in the south of France."
Balthus continued by saying he did not think it was tasteful to forcefully correct these errors, given his many Jewish friends. Nicholas Fox Weber concludes in his biography that Balthus was lying about this "biographical error," though the exact reasoning behind why was never explained. Weber states that the name "Spiro" is only a Greek given name, though this is incorrect, as the personal name serves equivalently as a surname. Balthus consistently repeated that if he, in fact, was Jewish, he would have no problem with it. In support of Weber's view, Balthus did make dubious claims about his ancestry before, once claiming he was descended from Lord Byron on his father's side.
According to Weber, Balthus would frequently add to the story of his mother's ancestry, saying that she was also related to the Romanov, Narischkin, and lesser known Raginet families among others, though conceding Balthus never claimed his mother's side was from a straight unmixed lineage. Despite the sensationalism with which Weber says he told these stories and the method in which Weber presents Balthus's claims, Balthus never saw himself as contradictory. The true extent of what Balthus was saying for artistic worth and what he was saying in earnest is unknown as he did not stick seriously to all his claims. Weber never interviewed Pierre Klossowski, the painter's brother, in order to confirm or deny their mother's ancestry. Weber did, however, present a quote by Baladine's lover, the poet Rainer Maria Rilke, in which Rilke states that the Spiros were descended from one of the richest Sephardic-Spanish families. In a seemingly conclusionary note, Weber writes: "The artist neglected, however, to tell me that, in the most miserable of ironies, Fumio (Balthus's son) suffered from Tay-Sachs disease." Weber holds this up as evidence that Balthus was lying about not having Jewish ancestry, given Tay-Sachs is a heavily Ashkenazic-Jewish disease. This, of course, conflicts with Rilke's report of the Spiros being Sephardic, which Weber later says was a "Rilke embellishment" and also brings up the relevance of the preponderance of Japanese infantile Tay-Sachs, since Balthus's wife was Japanese.
He has also influenced the filmmaker Jacques Rivette of the French New Wave. His film Hurlevent (1985) was inspired by Balthus's drawings made at the beginning of the 1930s. As he says in an interview with Valerie Hazette: "Seeing as he's a bit of an eccentric and all that, I am very fond of Balthus (...) I was struck by the fact that Balthus enormously simplified the costumes and stripped away the imagery trappings (...)".
A reproduction of Balthus's Girl at a Window (a painting from 1957) prominently appeared in François Truffaut's film Domicile Conjugal (Bed & Board, 1970). The two principal characters, Antoine Doinel (Jean-Pierre Léaud) and his wife Christine (Claude Jade), are arguing. Christine takes down from the wall a small drawing of approximately 25 x 25 cm and gives it to her husband: Christine: "Here, take the small Balthus." Antoine: "Ah, the small Balthus. I offered it to you, it's yours, keep it."
Robert Dassanowsky's book Telegrams from the Metropole: Selected Poems 1980-1998 includes a work titled "The Balthus Poem."
His widow, Countess Setsuko Klossowska de Rola, heads the Balthus Foundation established in 1998.