Elected to the House of Representatives in 1911, Hayden began a fifty-seven-year career in the U.S. Congress, serving as a Democratic House Representative for fifteen years and then as a Senator from 1927 to 1969.
The issues of the development of the Colorado River occupied the majority of Hayden's congressional work. The authorization of the Central Arizona Project (CAP) in 1968, at the end of the senator's long career, highlights all of Hayden's efforts concerning this lifestream of the Southwest, making possible the distribution of water to the growing urban areas of Phoenix and Tucson.