On March 11, 1893 in New Ulm, Minnesota, Wanda Gág was born to her parents Lizzie and Anton Gág. Her father and her mother's parents emigrated from Bohemia, a region in western Czechoslovakia. She lived in a creative household, and she and her six siblings danced, sang, and drew. In her father's skylighted studio, a large library and a collection of Native American artifacts and costumes shared space with his easel, paints, and works in progress. At age 15, her father passed away. On his deathbed, he told her in German, "What papa couldn't do, Wanda will have to finish."

Wanda Gág graduated high school in 1912 after which she taught country school for one year before attending St. Paul School of Art for one year and Minneapolis School of Art for three years. In 1916, her mother passed away. The next year, Gág won a scholarship to Art Students League of New York.

Wanda's first big break in the art world came in 1923 when the East 96th Street branch of the New York Public Library gave Gág her first one-artist exhibition. It included 19 drawings and 21 illustrations for children.

Her new major exhibition was held at Weyhe Gallery in 1928. Ernestine Evans, an editor at Coward-McCann, Inc., signed Gág to write Millions of Cats, after viewing the collection. From there she published ten children's books, illustrated one book for another author, and wrote an autobiography about her childhood.

Throughout these years she continued to create lithographs and watercolors, using an unusual print on sandpaper technique. In 1940 Edward Alden Jewell wrote on her artwork in the New York Times:

A room will writhe and twist and lurch, its furnishings as with some terrific inner compulsion, animate.

There is not a single static note. All is tenseness, quivering movement, drama—ideas externalized in an atmosphere of vehement light and dark.

Interiors are haunted by a presence that, if robustly sinister, is also diabolically humorous. It is a bewitched world that Wanda Gág portrays, but the bewitchment is tough, wiry, strong minded.

Wanda Gág died in New York City on June 27, 1946. She won the Newbery Honor Award and the Lewis Carroll Shelf Award for Millions of Cats, and the 1977 Kerlan Award for her entire body of work.