Pieck married twice. This union was dissolved on 14 May 1928. Pieck was the twin brother of Anton Franciscus Pieck, another Dutch painter and graphic artist. During the 1930s, Pieck operated as an agent for Soviet intelligence under Ignace Reiss.
After being arrested on 9 June 1941 for resistance activities, Pieck spent the rest of World World War II in German custody, first in the “Oranjehotel” (a detention center used at the beginning of the war by the Dutch as a Prisoner Of War camp that was later taken over by the Germans), after which he was deported to Buchenwald via the Nazi transit camp Amersfoort.