John Charles Fremont was born on January 21, 1813, in Savannah, Georgia. He received his education at the College of Charleston; he later taught mathematics aboard the warship Natchez. In 1840 Freemont married Jessie Benton, the daughter of a Senator.
Fremont was serving in the Army Topographical Corps when he had the opportunity to join the Nicollet expedition. While exploring the area, the expedition mapped the upper waters of the Missouri River. Freemont became a soldier, explorer, and political leader.
Soon Fremont was named as the commander of a second expedition to explore the western territories of the United States, the first being the Lewis and Clark Expedition. He explored Nebraska and Wyoming as an aid to settle Oregon. He embarked on an expedition in 1843 on which he crossed Wyoming and Idaho and explored Oregon and Nevada as well as parts of Arizona and Utah.
In 1844 Fremont explored California and helped to organize Americans in California to rebel against the Mexican authorities as part of the Mexican War. Fremont was elected as Governor of California on July 10, 1846, by American settlers, but he apparently did not serve his term of office. He was court-martialed by General Kearney, commander of United States forces in California over some controversy between the two men and resigned his commission. He embarked on a fourth expedition at his own expense; during this expedition he purchased the Mariposa Estate in California. His new estate was rich in gold mines, and he spent his time developing his estate.
Fremont took his seat in the United States Senate on September 10, 1850, one of the first two Senators from the State of California. In 1856 he was nominated as the first presidential candidate of the newly organized Republican Party, but he lost the election to James Buchanan. He resumed his military commission during the Civil War. In 1854 he was nominated for the office of President of the United States to run against Abraham Lincoln, but he withdrew.
From 1878 until 1881 Fremont served as governor of the Territory of Arizona. In the spring of 1890, Congress voted to place Fremont on the list of retired military officers; he received a comfortable salary until his death a few months later on July 13, 1890, in New York.