Nell Walker Warner (née Nellie Gertrude Walker), painter and illustrator, was born to Ida and William Walker in Richardson County, Nebraska on April 1, 1891. Her childhood was spent in Nebraska, Kansas, and after about 1902, in Colorado Springs, Colorado. She graduated from the Lexington Women's College in Missouri in 1910 and moved for a brief time to Colorado Springs on a teaching assignment. From there, Warner relocated to Los Angeles, California to enroll at the Los Angeles School of Art and Design, where she earned her degree in 1916.

Walker taught art classes at the Hollywood School for Girls and the Westlake School for Girls between 1916 and 1918. In 1919, she traveled to France, where she was introduced to Modernist ideas in painting. In the 1920 census, Walker’s employment is listed as being in the motion picture industry where she painted backgrounds for titles in silent films. In 1920 she married her first husband, surgeon Bion Smith Warner. They spent three summers traveling throughout Europe, where Warner sketched and painted landscape and harbor scenes in watercolor and gouache. During the years 1923 to 1925, Nell Walker Warner continued her studies with Nicolai Fechin and Fritz Werner.

In the 1930 census, Nell W. Warner is living in La Crescenta, Los Angeles and is listed as an artist in the industry of oil paintings. Ten years later in the 1940 census she is listed as living in Los Angeles with her occupation being a painter but her marital status is listed as widowed.

In October 1945 Warner married Emil Shostrom in Los Angeles and together they resumed extensive European and Latin American travels during the 1950s. In 1952, they settled in Carmel, where she became a member the Carmel Art Association and authored How Nell Walker Warner Paints in Oils, published in the Walter T. Foster instructional series in 1962. Warner was considered as “one of the ablest painters of flower studies America has ever produced.”

Warner was a life member of the Friday Morning Club of Los Angeles; second vice-president of the Women Painters of the West; past-president of the Glendale Art Association; and member of the Laguna Beach Art Association; the Academy of Western Painters; the California Art Club; the California Watercolor Society; the Society of Western Artists; and the Pasadena Society of Artists. In addition, she served as art curator for the Tuesday Afternoon Club in Los Angeles. Her work is represented in the collections of the Museum of Nebraska Art, Kearney; the Los Angeles County Museum of Art, California; and the Springville Museum of Art, Utah.

Nell Walker Warner died in Carmel, California on 20 November 1970.