Famous for the "Christy Girl" – a colorful and illustrious successor to the "Gibson Girl" – Christy is also widely known for his iconic WWI military recruitment and Liberty loan posters, along with his 1940 masterpiece titled, Scene at the Signing of the Constitution of the United States, which is installed along the east stairwell of the United States Capitol.

From the 1920s until the early 1950s, Christy was active as a portrait painter whose sitters included presidents, senators, industrialists, movie stars, and socialites.

Other famous people he painted include William Randolph Hearst, Edward VIII, Eddie Rickenbacker, Benito Mussolini, Prince Umberto, and Amelia Earhart.

Instead, he yearned for beauty and created the "Christy Girl", redefining the portrayal of women in America through his illustrations and portraits.

Having made his reputation for his work as a combat artist and in support of America's World War I effort, Christy soon was illustrating for numerous magazine covers.

His work, whether in watercolor, oils, or pen-and-ink, is characterized by great facility, a dashing but not exaggerated style and a strong sense of values.

Together with fellow artists Harrison Fisher and Neysa McMein he constituted the Motion Picture Classic magazine's "Fame and Fortune" contest jury of 1921–22, that discovered the It girl, Clara Bow.

Elise Ford was also Christy's model for the 1941 I Am An American poster personifying America "rushing forward to give the touch of the contagion of liberty and democracy to the rest of the world"[12] in the words of then New York Mayor Fiorello H. La Guardia.

[15] Attorney and author James Philip Head wrote a novelistic biography of Christy, The Magic of Youth, published in 2016.