[5] In 1941, he was invited by Stephen Wise and Nahum Goldman to join the Executive of the America Committee As an American Rabbi during The Holocaust, he often received reports from Nazi-occupied Europe.
One such report was that of the liquidation of the Warsaw Ghetto, in which he stated that "Nazis rolled through the streets in giant tanks, leveling stores and houses and silencing the feeble guns of the defenders, in the final stage of extermination..." and that "...every living soul was either butchered or uprooted and moved to some other part of the country.
He was a part of an interim committee of the American Jewish Congress and specifically oversaw the resettling of Jews in denazified Stuttgart.
[7] On November 14, 1949, Miller was elected as president of the American Jewish Congress, succeeding Stephen Samuel Wise.
After visiting the Jewish Center School in 1936, Eleanor Roosevelt wrote, “I wonder if many racial groups could not take a leaf out of their book, and if the result might not be far-reaching in making us understand other nations and what was drawn from them."