His father, Nicholas Platt, is an ex ambassador to Pakistan, Zambia, & the Phillipines.

Has an older brother, Adam Platt and a younger brother, Nicholas Platt Jr.

He is the son of Nicholas Platt (born October 3, 1936, New York, NY), a career American diplomat, and wife Sheila Maynard.

In the 1950s, his great-grandmother Cynthia Burke Roche resided at the famous Elm Court mansion in Newport, Rhode Island.

Avid Boston Red Sox fan.

He is also the paternal grandson of American architect Geoffrey Platt (by whom he has remote Dutch American ancestry) and wife Helen Choate.

His great-great-grandmother Frances Ellen Work's fortune was based on 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.

Three children: Lily (b. 1995), George (b. 1997), and Claire (b. 1999).

Since Diana Spencer was the great-granddaughter of the 3rd Baron Fermoy and Platt was his great-great-grandson, this makes him a second-cousin, once-removed, of Princess Diana, Princess of Wales. By extension, he is the third cousin of Prince William Windsor.

Attended Tufts University.

His mother, Sheila Maynard, was the daughter of 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) 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 son of the American heiress Frances Ellen Work), who was the maternal grandfather of Diana, Princess of Wales.

Was friends with "Huff" co-star Hank Azaria at Tufts University.

David E. Kelley originally wanted him to play the role of Bobby Donnell on the TV show "The Practice" (1997).

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.