Born in Huntsville, Utah, in 1915, Fawn Brodie came from patrician Mormon stock. Both her father, Thomas E. McKay, and uncle David O. McKay were important church leaders and her maternal grandfather, George H. Brimhall, was at one time president of Brigham Young University. A brilliant, precocious youngster, she graduated from Weber College, then a junior college, at the age of fourteen and from the University of Utah at age eighteen. She then returned to Weber College, where she taught for a year (1934-35) before leaving Utah in 1935 to attend the University of Chicago, where she received her M.A. in English in 1936 at age twenty. That same year she married Bernard Brodie, a native of Chicago of Latvian-Jewish stock and a fellow student, who completed his Ph.D. in international relations in 1940. They eventually became the parents of three children.

Following her move from Chicago to Hanover, New Hampshire, and then to Washington, D.C., Fawn Brodie did the research and writing for her first biography, the life of Joseph Smith, a task that consumed her energies for seven years. It was completed in 1945 following the Brodies' move to New Haven, Connecticut, and published under the title No Man Knows My History. A widely reviewed but extremely controversial work, this biography asserted that Mormonism's founder was in some respects a conscious fraud, and that in developing the doctrines associated with his movement, he was primarily influenced by ideas and forces in his nineteenth-century American environment. No Man Knows My History led directly to Brodie's excommunication from the Church of Jesus Christ of Latter-day Saints in May 1946.

In 1950 the Brodies moved to Pacific Palisades, California, where Fawn continued her writing. Her next two biographies, Thaddeus Stevens, Scourge of the South (1950) and The Devil Drives: A Life of Sir Richard Burton (1967), were lively accounts of their subjects but did not generate the controversy associated with her first work. In 1967 she joined the history department of the University of California at Los Angeles, where she remained until 1976. Meanwhile, she completed her fourth biography, Thomas Jefferson: An Intimate History (1974), a work which caused a storm within the Jefferson historical establishment comparable to that created by her Joseph Smith biography in the Mormon community three decades earlier. This was primarily due to Brodie's assertion that an intimate relationship existed between Jefferson and his black slave, Sally Hemings.

Brodie's fifth and final biography, Richard Nixon: The Shaping of His Character (1981), was completed as she was dying of cancer. It presented its subject in an extremely negative light, asserting that the personality of the disgraced ex-President was shaped by three major factors: the idea and fear of death, his trait as a pathological liar, and a lack of capacity to love. Even though Brodie did not live to see her Nixon biography in print, controversy surrounding this work and, indeed, her various other biographies has continued to the present, illustrating that her willingness to challenge the accepted was not the least of her own character traits and virtues.