[6] Thiebaud used heavy pigment and exaggerated colors to depict his subjects, and the well-defined shadows characteristic of advertisements were almost always included in his work.

[8] Morton was also a Ford mechanic, foreman at Gold Medal Creamery, traffic safety supervisor, and real estate agent.

[8] One summer during his first school years, he apprenticed at Walt Disney Studios[11] drawing "in-betweens" of Goofy, Pinocchio, and Jiminy Cricket at a rate of $14 a week.

On a leave of absence during 1956–57, he spent time in New York City, where he became friends with Elaine and Willem de Kooning[10] and Franz Kline, and was much influenced by these abstractionists as well as by proto-pop artists Robert Rauschenberg and Jasper Johns.

During this time, he began a series of very small paintings based on images of food displayed in windows, and he focused on their basic shapes.

These shows received little notice, but two years later, a 1962 Sidney Janis Gallery exhibition in New York officially launched Pop Art, bringing Thiebaud national recognition, although he disclaimed being anything other than a painter of illusionistic form.

[17] Stone said of Thiebaud "I have had the pleasure of friendship with a complex and talented man, a terrific teacher and cook, the best raconteur in the west with a spin serve, and a great painter whose magical touch is exceeded only by his genuine modesty and humility.

In 1962, Thiebaud's work was included, along with Roy Lichtenstein, Andy Warhol, Jim Dine, Phillip Hefferton, Joe Goode, Edward Ruscha, and Robert Dowd, in the historically important and ground-breaking "New Painting of Common Objects," curated by Walter Hopps at the Pasadena Art Museum (now the Norton Simon Museum at Pasadena).

Thiebaud employed heavy pigment and exaggerated colors to depict his subjects, and the well-defined shadows characteristic of advertisements are almost always included in his work.

[26][27] In addition to pastries, Thiebaud painted characters such as Mickey Mouse as well as landscapes, streetscapes, and cityscapes, which were influenced by the work of Richard Diebenkorn.

[28] His paintings such as Sunset Streets (1985) and Flatland River (1997) are noted for their hyper realism, and have been compared to Edward Hopper's work, another artist who was fascinated with mundane scenes from everyday American life.

[39] In November 2019, Sotheby's $8.46 million sale of Thiebaud's 2011 painting Encased Cakes set an auction record for the artist.

[40] This record was broken in July 2020, when his 1962 painting Four Pinball Machines sold for $19,135,000 in New York City at a Christie's global live auction event.