Planck managed to stay in favor with the Nazis for several years, but by the late 1930s, they had tired of him–and he of them. In 1936, Planck's enemies began to claim that he owed his fame solely to the so-called Jewish- Einstein conspiracy. Government sentiment turned against him, and though he was not driven from his posts, Planck resigned them all by 1938. Before he left, however, he was able to realize at least one dream. In 1938, Planck presided over the creation of a German Institute for Physics, which he had been working toward opening for a decade. Funding problems and political conditions had frustrated his efforts, but he finally reached his goal. In thanks to his tireless work and in recognition of his decades of contributions to German science, the institute was dedicated as the Max-Planck-Institut für Physik."

By this time, Planck was eighty years old, but he was by no means ready to retire. Instead, Planck began to wander the country, giving lectures on science, culture, and religion. Even then, Planck was careful not to say anything that might irritate the government.

But Planck was not destined to live out his final years in peace. War once again loomed on the horizon. Though Planck had by now completely disassociated himself with public life, his life was almost completely destroyed by World War II. On February 18, 1944, Planck's home was destroyed by an air raid. He lost everything: his library, his diaries and letters, and all of his possessions. Then, after learning that his granddaughter had tried to commit suicide, Planck was hit with the harshest blow of all. His only surviving child, Erwin, was accused of conspiring to assassinate Adolf Hitler. He was sentenced to death. Planck tried desperately to have Erwin's sentence commuted and was assured by a government official that a pardon was on its way. But on February 23, 1945, Erwin Planck was executed.

Planck was driven into a deep depression by his son's death, and his health declined severely. He suffered so much from back problems that he was often found screaming in pain. Planck and his wife settled briefly in a new home but soon found themselves surrounded by battle. Planck, now in his late eighties, was forced to flee his home and live in the woods.

Finally rescued by American officers, Planck went to live with his niece in Göttingen. The last few years of Planck's life had been marred by tragedy after tragedy, more in a short time than anyone could be expected to bear, and yet Planck refused to rest or relinquish his need to help others. At eighty-nine years old, he began once again to travel the country offering lectures because, as he explained, "what remains to me is the possibility of following the advances my work prepared and of responding to the wishes of people struggling for truth and knowledge, especially young people, by repeating my lectures here and there." To the very end, Planck believed that only in science could he–and his country–find redemption.

Planck died from a stroke on October 4, 1947. He left behind him an impressive legacy: father of quantum physics, spokesman of German science, defender of his people. And yet Planck was also one of the few preeminent scientists of the time to remain in Germany during World War II, to maintain a relationship with the Nazi regime. There are many who think that his inaction in these days was unjustifiable. Whether it was naiveté, miscalculation, or pure cowardice, Planck certainly could have done more. But he also could have done less. He was a moral man trapped in amoral circumstances, who perhaps failed to realize the consequence of the events going on around him. For Planck, politics always came second to science. This narrowed vision led him to his greatest achievements, but it also may have been his greatest failing.