Antoni Słonimski (15 November 1895 – 4 July 1976) was a Polish poet, journalist, playwright and prose writer, president of the Union of Polish Writers in 1956–1959 during the Polish October, known for his devotion to social justice.
Słonimski was the grandson of Rabbi Hayyim Selig Slonimski, the founder of the first Hebrew weekly ha-Tsefirah in Poland. His father, an ophthalmologist, converted to Christianity when he married a Catholic woman. Słonimski was born in Warsaw and baptized and raised as a Christian. Słonimski studied at the Academy of Fine Arts in Warsaw. In 1919 he co-founded the Skamander group of experimental poets with Julian Tuwim and Jarosław Iwaszkiewicz. In 1924 he travelled to Palestine and Brasil and in 1932 to the Soviet Union.
Słonimski spent the war years in exile in England and France, returning to Poland in 1951. He worked as contributor to popular periodicals: Nowa Kultura (1950–1962), Szpilki (1953–73) and Przegląd Kulturalny. He was an active anti-Stalinist and supporter of liberalization. Słonimski died on 4 July 1976 in a car accident in Warsaw.