Millard Sheets was born in Pomona, California. While growing up on a ranch, he developed a love for the foothills of Southern California. Sheets gained his early training as an artist the Chouinard Art School in Los Angeles from 1925-1929. He became acquainted with California artists John Chamberlin, Clarence Hinkle, and Theodore Modra. He also became exposed to the work American scene painter, Thomas Hart Benton and Grant Wood, who were pioneering a movement called American Regionalism. Like Wood and Benton, Sheets was interested in painting American daily life in and around the Los Angeles area.

Along with other California painters Milford Zornes, Rex Brandt, Phil Dyke, George Post, Millard Sheets developed the California Watercolor style of painting. These artists used watercolor instead of oil to paint on-site. Depicting daily life of everyday laborers, Sheets found watercolor and paper much more versitale and easy to transport than oil. Up until the 1920s, watercolor was seen simply as a sketching tool for artists, not a medium in itself.

Upon completing his schooling, Sheets decided to travel to Europe, where he became exposed to the modern aesthetic that was prevalent in Europe during the 1930s. Millard Sheets returned to California Sheets began teaching at Chouinard. During the Great Depression he began painting under the WPA as part of the team of muralist painters under the program. Sheets painted more than 100 murals around Claremont, Pomona, and greater Los Angeles. He also taught at Scripps College and Otis Art Institute, where he became an influential member of the art community. He was a member of the California Art Club; American Watercolor Society; Bohemian Club; National Academy.

His works are mostly landscapes of Pomona, Los Angeles, Laguna Beach, Santa Barbara, Palm Springs, and throughout California. Sheets eventually moved north to the Mendocino coast and painted throughout the Bay Area.