He went back to Procter and Gamble and became the products manager of the new foods division in 1955. Disillusioned with commerce, he took to journalism and joined the Paris bureau of United Press International in 1956, and became the news editor in Rome in the following year, and later the MidEast bureau chief in Beirut.
In 1965, Collins and Lapierre published their first joint work, Is Paris Burning? (in French Paris brûle-t-il?), a tale of Nazi occupation of the French capital during World War II and Hitler's plans to destroy Paris should it fall into the hands of the Allies. The book was an instant success and was made into a movie in 1966 by director René Clément, starring Kirk Douglas, Glenn Ford and Alain Delon.
In 1975, they published Freedom at Midnight, a story of the Indian Independence in 1947, and the subsequent assassination of Mahatma Gandhi in 1948. It is said they spent $300,000 researching and still emerged wealthy.
The duo published their first fictional work, The Fifth Horseman, in 1981. It describes a terrorist attack on New York masterminded by Libya's Colonel Gaddafi. The book had such a shocking effect that the French President cancelled the sale of nuclear reactors to Libya, even though it was meant for peaceful purposes. Paramount Pictures, which was planning a film based on the book, dropped the idea in fear that fanatics would emulate the scenario in real life.
In 1985, Collins authored Fall From Grace (without Lapierre) about a woman agent sent into occupied France who realizes she may be betrayed by her British masters if necessary. He also wrote Maze: A Novel (1989), Black Eagles (1995), Le Jour Du Miracle: D-Day Paris (1994) and Tomorrow Belongs To Us (1998). Shortly before his death, he collaborated with Lapierre on Is New York Burning? (2005), a novel mixing fictional characters and real-life figures that speculates about a terrorist attack on New York City.
In 2005, while working from his home in the south of France on a book on the Middle East, Collins died of a sudden cerebral haemorrhage.
In 1966, Collins married Egyptian princess Nadia Sultan. They had two sons, Michael and Lawrence.