MacArthur is the son of J. Roderick MacArthur and Christiane L’Entendart, and the grandson of billionaire John D. MacArthur. He grew up in Winnetka, Illinois, and graduated from Columbia College with a B.A. in history in 1978. He lives with his wife and two daughters in New York City.

Career

MacArthur has been a reporter for The Wall Street Journal (1977), the Washington Star (1978), The Bergen Record (1978—1979), Chicago Sun-Times (1979—1982), and an assistant foreign editor at United Press International (1982).

In 1980, MacArthur persuaded his grandfather's charitable foundation to partner in creating and funding a Harper's Magazine Foundation to acquire and operate the magazine of the same name. This new entity acquired Harper's Magazine (which was then losing nearly $2 million per year and was on the verge of ceasing publication) for $250,000. Eventually John R. MacArthur took over the foundation that owned Harper’s. He became president and publisher of Harper's Magazine in 1983.

In 1993 he received the Mencken Award for best editorial/op-ed column for his New York Times exposé of "Nayirah", the Kuwaiti diplomat's daughter who helped fake the Iraqi baby-incubator atrocity.