David E. Kelley originally wanted him to play the role of Bobby Donnell on the TV show The Practice (1997).
His father, Nicholas Platt, served as U.S. Ambassador to Pakistan, Zambia, and the Phillipines.
Attended Tufts University.
Three children: Lily (b. 1995), George (b. 1997), and Claire (b. 1999).
Has an older brother, Adam Platt, a New York Magazine restaurant critic, and a younger brother, Nicholas Platt, Jr.
Was a Boston Red Sox fan, but is now a New York Mets fan because his son likes the team.
Was friends with Huff (2004) co-star Hank Azaria at Tufts University.
High school graduate from the Colorado Rocky Mountain School in Carbondale, Colorado (near Aspen). The school's main curriculum is based on the "Outward Bound" education program, which teaches wilderness survival and expedition courses.
He is a paternal grandson of American architect Geoffrey Platt (by whom he has remote Dutch ancestry) and wife Helen Choate.
He is the son of Nicholas Platt (born October 3, 1936, New York, NY), a career American diplomat, and wife Sheila Maynard, a clinical social worker who worked in Islamabad.
His mother, Sheila Maynard, was the daughter of Walter Maynard and wife Eileen Burden Maynard Robins (October 15, 1910 - March 24, 1970), and a granddaughter of the Hon. Cynthia Burke-Roche (October 4, 1884 - August 12, 1966), who married (1) Arthur Scott Burden (August 11, 1879 - June 15, 1921), Oliver's great-grandfather, in 1906, and (2) Guy Fairfax Cary, Sr. (November 14, 1879 - August 27, 1950), in 1922. Cynthia was the sister of Edmund Maurice Burke-Roche, 4th Baron Fermoy in the Peerage of Ireland (of Irish and English extraction, and the son of American heiress Frances Ellen Work), who was the maternal grandfather of Princess Diana, of Wales.
A second cousin, once removed, of Princess Diana, of Wales. Diana was the great-granddaughter of the 3rd Baron Fermoy and Platt was his great-great-grandson. By extension, he is a third cousin of Prince William.
His great-great-grandmother Frances Ellen Work was heir to a maternal pork-packing fortune created in Chillicothe, Ohio, and a paternal dry good and finance fortune created in New York City. Her father Frank's fortune was estimated at $15 million, and he served as stockbroker to Commodore Vanderbilt.
In the 1950s, his great-grandmother Cynthia Burke Roche resided at the famous Elm Court mansion in Newport, Rhode Island.
He has English, and smaller amounts of Irish, Dutch, and French, ancestry.
Making his Broadway debut in Conor McPherson's Shining City, at the Biltmore Theatre on Broadway. His brilliant performance was honored with a Tony nomination for best actor. [June 2006]
Appeared in three movies with Kevin Bacon: Flatliners (1990), Frost/Nixon (2008) and X-Men: First Class (2011).
His paternal great-grandfather was landscape gardener/designer, artist, and architect, Charles A. Platt, and among his great-great-grandfathers are diplomat and lawyer Joseph Hodges Choate (on his father's side) and general Robert Shaw Oliver (on his mother's side).
He is missing the end knuckle from the middle finger on his right hand. He got it caught in the wheel of a generator when he was 12 years old during a tour with his father in China.