Lionello Venturi (25 April 1885, Modena – 14 August 1961, Rome) was an Italian historian and critic of art. He produced the first catalogue raisonné of Paul Cézanne.
Lionello Venturi was born in 1885, son of art historian Adolfo Venturi. He became a specialist in the art of the Italian Renaissance, but was also interested in late 19th and early 20th century art. In 1918 he met the financier and collector Riccardo Gualino, and advised him to buy work by Amedeo Modigliani. Gualino and Venturi supported Turin painters such as Felice Casorati and the Gruppo di Sei (Group of Six), which included Carlo Levi, Francesco Menzio, Jessie Boswell, Gigi Chessa, Enrico Paolucci and Nicola Galante. Venturi was appointed Professor of Art History at the University of Turin in 1919. One of his first students there was Mary Pittaluga, who wrote her thesis on Fromentin under Venturi. In 1930 Venturi organized a retrospective exhibition of Modigliani's work in Venice based on the paintings owned by Gualino.
Though appointed his father's successor in the art history chair at the University of Rome in 1931, Venturi refused to swear allegiance to Benito Mussolini's regime in August 1931 and so was forced to resign from the university. He left Italy, initially moving to Paris, where he wrote, advised art dealers and museum curators, and produced the first catalogue raisonné of Paul Cézanne. After the establishment of the Vichy regime, he emigrated to the United States, living in New York City until 1945 and lecturing at a range of American universities. While in America, he joined the antifascist Mazzini Society. After the war he returned to Italy, taking up his chair in art history at Rome.