Valtin became active in the Communist movement as a boy, when his father was involved in the naval mutiny that heralded the 1918 German revolution. In 1923, he saw action in the failed Communist insurgency in Hamburg. Sometime after this he was recruited by the GPU, the foreign intelligence service of the Soviet Union, and forerunner to the KGB. Valtin/Krebs married again, before 1941, to Abigail Harris, an American. They had two sons.