James Alexander McDougall was born on November 19, 1817 in Bethlehem, New York and educated in the Albany grammar schools, where he excelled in mathematics and civil engineering. While still a young man, McDougall assisted the survey of the Mohawk and Hudson Railroad, later known as the Albany and Schenectady, one of the first railroads in the nation. McDougall began the study of law in Albany before moving westward, settled in Pike County, Illinois in 1838, married the daughter of a leading Jacksonville attorney, and joined the Democratic Party. He completed his study and began practicing law in Cook County, where McDougall soon made the acquaintance of another rising Chicago lawyer, Stephen A. Douglas.
In January 1843 the 25-year-old McDougall was elected Illinois Attorney General; he was re-elected in 1844. "Small in stature, he had uncommon strength of constitution, as well as of mind. He was a brilliant speaker, skillfully wielding the weapons of repartee, humor, and sarcasm, and made himself one of the most noted speakers of the West." During his tenure in the state capitol, Springfield, Illinois, rising tensions in Nauvoo, Illinois gave way to violence when on June 27, 1844, the founder of the Latter Day Saint movement, Joseph Smith was killed by a mob after surrendering to the custody and protection of the state. McDougall was involved in the negotiations by which the Mormons agreed to leave Illinois. Following his two terms as state attorney general, McDougall returned to private practice in Chicago, establishing a law partnership with Ebenezer Peck.
While traveling the circuit and serving as attorney general in Illinois, McDougall became friendly with many fellow lawyers, including Douglas, Edward D. Baker and Abraham Lincoln. By 1849, McDougall had been twelve years in the Prairie State of Illinois, and had made himself "one of the most popular men of his state," but like many of his age was still looking westward. McDougall organized and accompanied an exploration of the Rio del Norte, Gila and Colorado Rivers reaching the headwaters of the Rio Grande in what would soon become southwestern Colorado Territory. Hearing news of the California Gold Rush, McDougall returned to Illinois, gathered up his family and possessions, and took the new steamship California to San Francisco.
Resuming his law practice, McDougall was elected California Attorney General in October 1850 but resigned after a year to accept a seat in the state legislature.
In 1852 McDougall successfully ran for Congress as a Democrat, pledging to get federal support for a railroad to the Pacific. He did introduce a Pacific Railroad bill, but it was opposed by Thomas Hart Benton. McDougall served a single term in the House before returning to law practice in San Francisco.
The Democrats in California split into factions, and election of a California Senator in 1860 became entangled in the national crisis over secession. When it appeared that a secessionist Democrat might be elected, Republicans abandoned their own candidate and threw their support to McDougall.
While serving in the U.S. Senate during the Civil War, McDougall again worked on behalf of a Pacific railroad project, but alcohol abuse made him ineffective. By 1862, McDougall was making a spectacle of himself and neglecting his Senate duties. He fought against some of Lincoln's war measures, but he was mostly dysfunctional. Not once did he travel back to California during his entire six-year term.
Upon leaving office, McDougall retired to his boyhood home in Albany, New York, where he died on September 3, 1867, presumably of alcoholism. His body was sent to California, per his wishes, and buried in Lone Mountain Cemetery in San Francisco, later renamed Calvary; his remains were reinterred at Holy Cross Cemetery in Colma, California in 1942.