Eugeniusz Żak was born to a family of assimilated Polish Jews. As a boy he moved to Warsaw, where he graduated from a non-classical secondary school. In 1902, he left for Paris to undertake studies, first at the École des Beaux-Arts in the studio of the aged master of academism Jean-Léon Gerôme, and then at Académie Colarossi in the studio of Albert Besnard.
In 1903, he traveled to Italy and toward the end of the year to Munich, where he entered a private school run by the Slovenian Anton Ažbé. His fame grew rapidly. The French government purchased of one of his paintings for the Luxembourg Museum (1910), he organized a one-man show at Galerie Druet (1911), and he was connected with important personalities of Parisian cultural life, including the critics Adolf Basler and André Salmon. In 1912 he became a professor at the Académie La Palette. In 1913 he married a beginning painter Jadwiga Kon, who managed the well-known Galerie Zak after his death.In 1916 he returned with his family to Poland, settling in his wife's hometown of Częstochowa. He associated with the Formists. Upon his frequent visits to Warsaw, he collaborated with the future members of Rhythm, a group he co-founded in 1921. In 1922 he left Poland for good. First, he went to Germany, where he had already been known and esteemed before the World War I. He visited Berlin and later Bonn, where he carried out a commission to decorate the interior of the villa of the architect Fritz August Breuhaus with paintings. He co-operated with the periodical Deutsche Kunst und Dekoration, publishing articles on certain artists who were close to him. In 1923 he settled once again in Paris, where he joined his friends Zygmunt Menkes and Marc Chagall. His growing artistic fame and financial successes ended suddenly when he died of a heart attack. He did not live to take over the faculty of painting, which had been offered to him by the Academy of Fine Arts, Cologne, Germany.