His mother was a member of the New England Sedgwick family and a descendant of American Civil War heroes. He studied at Harvard, where he composed football songs, and there became acquainted with Walter Lippmann, John Reed, and Roosevelt, a distant cousin. On February 11, 1920, he married Helene Niemayer/Helen Neemeyer of Long Island. They had a daughter, who died young, and a son, Egon, who joined the US Army.
He later returned to Germany and became friends with Adolf Hitler, who called him "Putzi". He wrote Brownshirt marches based on his Harvard football songs. After the 1923 Beer Hall Putsch he sheltered Hitler in his attic. Helene reputedly prevented Hitler from killing himself.
He financed the publication of Mein Kampf and claimed to have participated in the firing of the Reichstag. He became head of the Foreign Press Bureau in Berlin, but aside from his official position his importance lay in the fact that he entertained Hitler, who relaxed when "Putzi" played the piano.
He divorced Helene in 1936, and fled Germany in March 1937 after becoming disenchanted with Hitler. After first escaping to Switzerland, he moved to England, where he was imprisoned as an enemy alien after the outbreak of World War II; he was later moved to a prison camp in Canada. In 1942 he was turned over to the U.S. (possibly on Roosevelt's personal intercession), but was handed back to the British in 1944, who returned him to Germany after the end of the war.
He wrote Unheard Witness (1957) about his experiences.