He became the first president of the , inaugurated in September 1943, inspired (and encouraged) by the inauguration of an equivalent organisation by exiled German communists in Moscow a couple of months earlier. This brought him into contact with Willi Kreikemeyer and in connection with fund transfers from the United States of America through the mysterious Noel Field. Niebergall also worked closely with the remarkable Luise Kraushaar who is described in at least one source as his secretary during much of his time with the French Resistance. He remained the organisation's president even after the 1944 liberation of Paris in which he participated, and following which the C.A.L.P.O. ceased to be illegal in newly liberated parts of France and - at least in the Paris region which quickly became a magnet for refugees from further east - transformed itself into a desperately needed welfare organisation, providing support for the most acutely needy war victims. An important priority, even under circumstances in which communication could be hugely challenging, was for covert co-ordination to maintain contact with resistance groups inside Germany. It later became clear that during the fighting which preceded to the liberation of Paris in August 1944 he was in contact with resistance activists inside Germany plotting to assassinate Hitler.