Quinn was an important patron of chief figures in Post-impressionism and literary Modernism; a major collector of modern art and original manuscripts; and the first to exhibit these works after winning legal battles against censorship and cultural isolation. In the 1920s he owned the largest single collection of modern European paintings in the world. He fought key legal battles that opened American culture to 20th century art movements, including his Congressional appeals to overturn the Payne–Aldrich Tariff Act. He was part of the group who staged the Armory Show, the first great exhibition of European and American modern art in the United States at the 69th Regiment Armory, New York, in 1913. Quinn gave practical advice and financial assistance to Ezra Pound and T.S.Eliot. In gratitude, Eliot sent Quinn the original manuscript of his poem "The Waste Land", including Pound's editorial suggestions.