William McKendree Gwin was born on October 9, 1805 near Gallatin, Tennessee. William's father, a Weslshman, had come to the United States shortly after it gained independence from England and settled first in Charleston, South Carolina. As Daniel Boone and other frontiersmen opened new lands to the west he moved to Tennessee where he became a Methodist preacher and befriended Andrew Jackson. In the war of 1812 he commanded 1400 frontiersmen at the Battle of New Orleans. (The American rifle proved far superior to the British musket and played an important role in Jackson's victory.)
Early on, William was interested in studying law, but decided that the field was too crowded with older men already well established. He turned to the study of medicine instead and graduated from the Medical Department of the Transylvania University in Lexington, Kentucky in 1828. Following school he served as President Jackson's private secretary in Washington for six months in 1831. After his stint in the White House, at Jackson's urging, he moved to Clinton, Mississippi and established a medical practice. In 1833 Jackson appointed Gwin United States marshal in Mississippi and charged him with building a pro-Jackson wing of the Democratic Party in the state. While in Mississippi he purchased a plantation and engaged in very large scale and very profitable land speculation in that state and in Texas. Gwin met his wife Mary through Sam Huston, another pro-Jackson family friend from Tennessee.
In 1841 Gwin was elected to the House of Representatives from Mississippi and spent his two year term working hard to avoid bankruptcy due to failures in some of his land deals. While in Washington, Gwin became personal friends with John Calhoun. They disagreed on the issue of Nullification, but Gwin was very impressed with Calhoun's support of Manifest Destiny and the importance that he saw for California once it was taken from Mexico. States Rights was one of the more important issues of the day in Mississippi and Gwin was on the wrong side of the argument. Jefferson Davis was selected to take his seat in the House in 1843, but it did not cause a riff between the two men. Davis and Gwin remained personal friends. James K. Polk, a Jacksonian Democrat, was president and the Democratic Party continued to think highly of Gwin. At the end of the Mexican War he was the Commissioner of Public Works for the Port of New Orleans - a very lucrative position.
Zachary Taylor, a Whig, replaced Polk in the White House and Gwin went to Washington for his inauguration on March 5, 1849. Gwin consulted with his political allies and decided to go to California to build up the Democratic Party in that state. On June 4, 1849, he arrived in San Francisco on the steamship Panama. (Jessie Fremont was also aboard as was President Taylor's personal representative Thomas Butler King.) Events were moving rapidly. Congress had failed to decide on how California was to be governed and the military governor, General Bennet Riley, called for the election of representatives to a constitutional convention to decide the issue. Both King and Gwin stumped the state during the election. Gwin used the election campaign to recruit a coterie of supporters that became the core of his wing of the Democratic Party in California. Most of them were southerners and they became know as the "Chivalry."
In July 1849 Gwin served as one of the vigilante judges that dealt with the individuals who had rioted against Hispanics in San Francisco. In this very public endeavor he was allied with Sam Brannan and many of the more established elements of the community. During the Constitutional Convention in October 1849 Gwin served as Chairman of the Committee charged with drawing up the new constitution. Following the completion of the convention and its acceptance of the newly drafted constitution, Gwin hit the hustings again to ensure the passage of the constitution and to campaign for Chivalry members to be elected to the new state legislature. In those days the legislature selected the men who would represent the state in the United States Senate. Gwin wanted one of the two seats. He had his work cut out for himself because the leading contenders in the senate race were the very popular Fremont, an abolitionist, and King, a prominent Whig friend of President Taylor.