John Treadwell Nichols (born July 23, 1940, Berkeley, California) is an American novelist. He is the author of the "New Mexico trilogy", a series about the complex relationship between history, race and ethnicity, and land and water rights in the fictional Chamisaville County, New Mexico. The trilogy consists of The Milagro Beanfield War (which was adapted into a movie of the same title directed by Robert Redford), The Magic Journey, and The Nirvana Blues.

Two of his other novels have also been made into films. The Wizard of Loneliness was published in 1966 and the film version with Lukas Haas was made in 1988. Another successful movie adaptation was of The Sterile Cuckoo, which was published in 1965 and was filmed by Alan J. Pakula in 1969. He also had an important but uncredited hand - due to a Writers Guild arbitration decision - in the Oscar-winning Best Adapted Screenplay for Costa-Gavras' 1982 film, Missing.

Nichols has also written non-fiction, including the trilogy If Mountains Die, The Last Beautiful Days of Autumn and On the Mesa. John Nichols has lived in Taos, New Mexico for many years. He is the subject of a documentary The Milagro Man: The Irrepressible Multicultural Life and Literary Times of John Nichols, which premiered at the 2012 Albuquerque Film Festival.

Nichols is the grandson of ichthyologist John Treadwell Nichols and a first cousin of Massachusetts politician William Weld.