Just was born in Michigan City, Indiana, attended Lake Forest Academy, and subsequently graduated from Cranbrook School in 1953. He briefly attended Trinity College in Hartford, Connecticut. He started his career as a print journalist for the Waukegan News-Sun. He was also a correspondent for Newsweek and The Washington Post from 1959 to 1969, after which he left journalism to write fiction.
His influences include Henry James and Ernest Hemingway. His novel An Unfinished Season was a finalist for the Pulitzer Prize for Fiction in 2005. His novel Echo House was a finalist for the National Book Award in 1997. He has twice been a finalist for the O. Henry Award: in 1985 for his short story About Boston, and again in 1986 for his short story The Costa Brava, 1959. His fiction is often concerned with the influence of national politics on Americans' personal lives. Much of it is set in Washington D.C. and foreign countries. Another common theme is the alienation felt by Midwesterners in the East.
According to Washington Post book critic Jonathan Yardley, Just's three finest novels are A Family Trust, An Unfinished Season and Exiles in the Garden.