Egan was born in Detroit, Michigan, and served in the United States Navy during World War II. After the war, he studied journalism at the University of Southern California. In 1948, he moved to New York City, where he worked as a playwright and screenwriter.
Egan's first novel, The Enormous Room, was published in 1953 and was a critical success. The novel tells the story of a young American man who is imprisoned in a fascist prison in Italy during World War II.
He wrote more than 20 books:
- The Enormous Room (1953)
- City Without Jews (1957)
- Edge of the World (1960)
- All the Love in the World (1962)
- The Death of a Gentleman (1963)
- Never Call it Love (1965)
- The Last One Left (1967)
- An Ill Wind Blows (1969)
- The Judas Time (1970)
- The Night in Question (1972)
- The Winter People (1973)
- The Wine of Violence (1974)
- The Blind and the Beautiful (1976)
- The Price of Diamonds (1978)
- The Gold Pen (1980)
- The Silver Dagger (1982)
- The Ruby Ring (1984)
- No Time for Love (1986)
- The Love Affair (1988)
- Time of the Cobra (1991)
- The Woman Who Knew Too Much (1994).