James Henry Mays was born 29 June 1868 in Morristown, Hamblen County, Tennessee. He moved with his family in 1883 to Kansas, where he attended the Kansas State Normal School. He worked his way through the school by putting up timbers in lead and zinc mines and by teaching school. He graduated from the University of Michigan law department in 1895 and was admitted to the Michigan bar. He practiced law for a short time in Michigan before moving to Indianapolis, Indiana, in 1896 and then to Utah in 1902.

Mays married Sarah Elizabeth Randels, and they were the parents of five children. His interests turned to mining, and in association with other men he developed Castle Valley coal properties, becoming president and director of the Castle Valley Coal Company. He successfully fought the Denver and Rio Grande Western Railroad and its subsidiary coal companies through the Interstate Commerce Commission and won an outlet for his coal with the victory.

In college James Mays was a distinguished debater, and in later years he was considered to be one of the most forceful and logical speakers in the state. His first political honors came unsolicited when he was nominated by the Progressives and Democrats and then elected to the Sixty-fourth Congress. He served three terms in the United States House of Representatives from 1914 to 1920, and was not a candidate for reelection in 1920. After leaving Washington, Mays retired to his stock range near Wendell, Idaho. He spend considerable time and means developing his extensive coal-mining projects in Huntington Canyon, Emery County, and also developing a power site near his ranch in Idaho. Mays died at his ranch on 19 April 1926 following a stroke and was buried in the Gooding Cemetery, Gooding, Idaho.