He is best known for his work as an illustrator and cartoonist, particularly for his creation of the character 'The Yellow Kid,' which was first published in 1895 in the New York World newspaper. Outcault's artwork often featured children and everyday life, showcasing a strong sense of observation and attention to detail.

His artistic style was characterized by simplicity, directness, and an emphasis on storytelling. As one of the pioneers of American Realism, Outcault's influence can be seen in many subsequent artists who followed in his footsteps. Some of his notable works include 'The Yellow Kid' series, as well as illustrations for other publications such as Life magazine.

Today, Outcault is recognized as a significant figure in American art history, and his contributions to the development of Realism continue to be celebrated.