Jessie Benton Fremont was born near Lexington, Virginia and raised in Washington, D.C., the daughter of Senator Thomas Hart Benton of Missouri and his wife Elizabeth McDowell. Her father supervised her early education and introduced her to the leading politicians of that time, as well as to his vision of a USA stretching from ocean to ocean. She became fluent in French and Spanish and helped her father by translating secret documents for the State Department, and serving as his hostess .
In 1841, at age 17, she married Lieutenant John C. Fremont, an officer in the army's Topographical Corps, over objections from her parents that she was too young; they would have five children. Frémont became known as the "Pathfinder to the West" for his expeditions, and Jessie became his secretary, writing up notes and reports on his experiences. She then wrote and edited bestselling stories of his adventures exploring the West with Kit Carson, his scout. In 1849, she and her young daughter made a harrowing voyage to join Fremont in California and the family settled in San Francisco. She became politically active and supported her husband's successful run for a Senate seat in 1850. In 1856, Fremont's became the first Republican candidate for President, and Jessie played an important role in the campaign, which ultimately lost to James Buchanan. President Lincoln appointed Frémont as Commander of the Department of the West in 1861, and the couple moved to St. Louis, where Jessie served as her husband's unofficial aide and closest adviser. During the Civil War, she devoted herself to relief efforts. After the war, they lived in New York and then California. After they lost all their money on railroad stocks, Jessie wrote articles and stories for leading magazines and books to help support the family, including A Year of American Travel: Narrative of Personal Experience (1878), Souvenirs of My Time (1887), and Far-West Sketches (1890). She was also the principal writer of her husband’s Memoirs of My Life (1887).