Stavros Niarchos III (born 17 April 1985) is a professional kiteboarder and an heir to a Greek shipping fortune.

Niarchos is of Greek, Irish, Austrian, and Mexican ancestry, Niarchos was born in New York City and grew up in Paris, France. He is the elder son of Philippe Niarchos and his third wife, the former Victoria Guinness, herself the granddaughter of the socialite Gloria Guinness. His namesake grandfather, shipping tycoon Stavros Niarchos, was a rival of Aristotle Onassis.

Niarchos is a first cousin, once removed of Athina Onassis, whose maternal grandmother, Tina Onassis, was Niarchos's great-aunt as well as the fifth wife of his paternal grandfather. The Aga Khan IV is his great-uncle. his sister is the jewelry designer and socialite Eugenie Niarchos (born 1986).

Stavros Niarchos was a student in the Collège Stanislas in Paris. His senior year of high school was spent at Seabury Hall, a college preparatory school located in Makawao on Maui, Hawaii. After high school, Niarchos attended the University of Southern California Film School where he graduated and received his diploma in May of 2007.

A tall, athletic blond, Niarchos is best-known for dating Paris Hilton, Mary-Kate Olsen and Lindsay Lohan. He also appeared with actress Kate Bosworth in her January 2005 GQ magazine spread.