Born 1875 to Jewish parents in Iaşi, Romania. In 1892 Segal studies at the Academy of Art in Berlin, taking master classes with Eugen Bracht. Two years later he continues his studies at the Académie Julien in Paris, attending Ludwig Schmid-Reutte and Friedrich Fehr’s painting school in Munich one year later, after which he takes up studies with Carl von Marr at the Academy of Art in Munich, where he is active as a freelancer from 1899 before moving to Berlin in 1904 and taking part in the 1909 and 1913 exhibitions of the Berliner Secession. His first woodcuts are published in Herwarth Walden’s Der Sturm in 1911, followed a year later by an exhibition in Walden’s eponymous art gallery.
In 1914 he emigrates to Ascona and becomes acquainted with Hans Arp, Alexei von Jawlensky, Hugo Ball, and Leonhard Frank. In 1916 he has an exhibition at the Cabaret Voltaire of the Zurich Dadaists, returning in 1920 to Berlin where he opens his own painting school, with Nikolaus Braun and Lou Albert-Lasard among his students. He is a member of the Novembergruppe (November Group), being on its board of directors for some time and repeatedly participating in the group’s exhibitions from 1921 to 1931. His Berlin studio is the place of regular meetings of Adolf Behne, Raoul Hausmann, Hannah Höch, Kurt Schwitters, and George Grosz. Together with Otto Dix, George Grosz, and Käthe Kollwitz among others he is active in the trade unions’ campaign "For an eight-hour-day". In 1925 he is the co-publisher with Nikolaus Braun of the treatise Lichtprobleme der Bildenden Kunst (On the Problem of Light in the Fine Arts).
In 1925 he was offered a teaching job in New Bauhaus in Dessau, but he declined. Because of his Jewish background he was prevented from exhibiting his work in Germany, and so in 1933 he moved to Palma, Mallorca and three years later to London where he opens a painting school with his daughter Marianne. In 1944 he dies of heart failure during a bombing raid of the German Luftwaffe.