Oliver Platt was born in Windsor, Ontario, Canada. His place of birth is often reported as Washington because that is where his parents resided at the time. His parents are Sheila Maynard, a former clinical social worker in Islamabad, and Nicholas Platt who served as the U.S. Ambassador to Zambia, the Philippines, and Pakistan. Oliver is the middle child of three sons. His older brother Adam is a writer for New York Magazine and his younger brother Nicholas Jr. is a publishing executive.
Due to his father's diplomatic career, Oliver Platt's family moved to many different places, including the Middle and Far East, and he attended many different schools. In 1983, he earned his Bachelor of Arts degree with a major in Drama from Tufts University, Massachusetts.
In September 1992, Oliver Platt married Mary Camilla Bonsal Campbell at the First Congregational Church in Kittery Point, Maine. Camilla Campbell works as a freelance assistant producer of documentary films in New York. They have three children, Lili (born in 1994), George (born in 1997), and Claire (born in 1999).
Oliver Platt is mainly a movie actor and says that he enjoys playing interesting supporting roles. His major tv credits include the Award-winning role as Russell Tupper in Huff and recurring roles in The West Wing and Bored To Death.