Kuhn was born in Brooklyn, New York City. At 15, Kuhn sold his first drawings to a magazine and signed his name “Walt.” In 1893, he enrolled in art classes at the Brooklyn Polytechnic Institute.
In 1899, Kuhn set out for California with only $60 in his pocket. Upon his arriving in San Francisco, he became an illustrator for WASP Magazine. In 1901, Walt left for Paris, where he briefly studied art at the Académie Colarossi before leaving to the Royal Academy in Munich. Once in the capital of Bavaria, he studied under Heinrich von Zugel (1850–1941), a member of the Barbizon School.
In 1903, he returned to New York and was employed as an illustrator for local journals. In 1905, he held his first exhibition at the Salmagundi Club, establishing himself as both a cartoonist and a serious painter. In this same year, he completed his first illustrations for LIFE magazine.
When the New York School of Art moved to Fort Lee, New Jersey in the summer of 1908, Kuhn joined the faculty. However, he disliked his experience with the school, and at the end of the school year, he returned to New York. There, he married Vera Spier. Soon after a daughter, Brenda Kuhn, was born.
In 1909, he helped prepare his first solo-exhibition in New York. In the following years, Kuhn took part in founding the Association of American Painters and Sculptors- the organization responsible for the Armory Show of 1913. Kuhn acted as the executive secretary and was put in charge of finding European artists to participate. The Armory Show, which displayed both European and American modern art to New York audiences, proved to be both a controversy and triumph. Smart and sensational publicity, combined with strategic word-of-mouth, resulted in attendance figures over 200,000 and over $44 thousand in sales. The Armory Show had demonstrated that modern art had a place in the public taste, that there was a market for it.
In 1925, Kuhn’s health had turned for the worse when he almost died from a duodenal ulcer. After an arduous recovery, he became an instructor at the Art Students League of New York. He also completed a commission for the Union Pacific Railroad, the club car “The Little Nugget” LA-701, currently under restoration at the Travel Town Museum in Los Angeles, California. In 1933, the aging artist organized his first retrospective.
By the 1940s, Kuhn’s behavior began to take on unsound characteristics. He became increasingly distant, and when the Ringling Brothers Circus was in town, he attended night after night. In 1948, he was institutionalized, and on July 13, 1949, he died suddenly from a perforated ulcer.