Bagley was born at Kendal, Cumbria (then Westmorland), England, the son of John and Hannah Bagley. His family moved to the resort town of Blackpool in the summer of 1935, when Bagley was twelve. Leaving school not long after the relocation, Bagley worked as a printer's assistant and factory worker, and during World War II he worked in the aircraft industry. Bagley suffered from a speech impediment (stuttering) all of his life, which initially exempted him from military conscription.

He left England in 1947 for Africa and worked his way overland, crossing the Sahara Desert and briefly settling in Kampala, Uganda, where he contracted malaria. By 1951, he had settled in South Africa, working in the gold mining industry and asbestos industry in Durban, Natal, before becoming a freelance writer for local newspapers and magazines.

His first published short story appeared in the English magazine Argosy in 1957, and his first novel, The Golden Keel in 1962. In the interval, he was a film critic for Rand Daily Mail in Johannesburg from 1958—1962. Also during this period, he met local bookstore owner Joan Margaret Brown and they were married in 1960.

The success of The Golden Keel led Bagley to turn full time to novel writing by the mid-1960s. He published a total of sixteen thrillers, all craftsmanlike and nearly all best-sellers. Typical of British thriller writers of the era, he rarely used recurring characters whose adventures unfolded over multiple books. Max Stafford, the security consultant featured in Flyaway and Windfall, is a notable exception. Also typically, his work has received little attention from filmmakers, yielding only a few, unremarkable adaptations. Exceptions were The Freedom Trap (1971), released in 1973 as The Mackintosh Man by Warner Brothers, starring Paul Newman and Dominique Sanda; and Running Blind which was adapted for television by the BBC in 1979.

In several novels Bagley used the first-person narrative. One reviewer wrote: "as long as meticulous craftsmanship and honest entertainment are valued, and as long as action, authenticity, and expertise still make up the strong framework of the good adventure/thriller, Desmond Bagley's books will surely be read."

Bagley and his wife left South Africa for Italy in 1960, and then England in 1965. They settled in Totnes, Devon from 1965—1976, then lived in Guernsey in the Channel Islands from 1976-1983.

Bagley also published short stories. When not traveling to research the exotic backgrounds for his novels, Bagley spent his time sailing and motor-boating. He loved classical music and films, military history, and played war games.

Desmond Bagley died of complications resulting from a stroke at a hospital in Southampton. He was fifty-nine. His last two novels Night of Error and Juggernaut were published posthumously after completion by his wife. His works have been translated into over 20 languages.

Dates are for first UK hardcover publication; all of Bagley's novels subsequently appeared in paperback.

• The Golden Keel (1962)
• High Citadel (1965)
• Wyatt's Hurricane (1966)
• Landslide (1967) (made into the 1992 film of the same name)
• The Vivero Letter (1968) (made into the 1998 film of the same name.)
• The Spoilers (1969)
• Running Blind (1970)
• The Freedom Trap (1971) (made into the 1973 film The Mackintosh Man)
• The Tightrope Men (1973)
• The Snow Tiger (1975)
• The Enemy (1977) (made into the 2001 film The Enemy)
• Flyaway (1978)
• Bahama Crisis (1980)
• Windfall (1982)
• Night Of Error (1984)
• Juggernaut (1985)