Hahn was the fifth daughter born to Isaac and Hannah Hahn, who encouraged independence in their daughters. Her mother was an advocate of equal rights for women. The family moved to Chicago when Hahn was 15, but she moved back to St. Louis after graduating from college. She was the first woman to graduate from the University of Wisconsin-Madison’s College of Engineering. Her job in St. Louis was at the mining company, McBride Inc, but since she was only given secretarial duties, she quit after a year.

Hahn loved to travel. As a sophomore in college, she and a girlfriend drove 2,400 miles from Wisconsin to California in a Model T. She pledged that if Lindbergh’s plane, "The Spirit of St. Louis," crossed the Atlantic successfully, she would continue her travels. True to her word, she went to New York, London, the Belgian Congo, Bombay, Nairobi, Shanghai and Hong Kong. She wrote more than 50 books, and became a leading correspondent.

During her seven years in China, she married poet and publisher Sinmay Zau, overcame an opium condition, and had a child out of wedlock with British intelligence officer Charles Boxer, which was one of the great scandals of World War II. He was captured during the war and, after his release from a Japanese prisoner-of-war camp in 1945, he divorced his wife, married Hahn and had a second child with her. Hahn continued to write until 1996.