Courtney Ryley Cooper was born in Kansas City, Missouri on October 31, 1886. At the age of 16, he left home to join a traveling circus and eventually became a circus clown, working his way up to general manager of the circus.

Later, he worked as a newspaper reporter for The Kansas City Star, New York World, the Chicago Tribune and the Denver Post. In 1914, as a result of his work at the Post, he became the press agent for the Sells-Floto Circus, which was owned by the owners of the Post. The Sells-Floto had absorbed the assets of William "Buffalo Bill" Cody's Wild West Show, including Buffalo Bill himself.

On August 1, 1918, Cooper joined the United States Marine Corps. He rose to the rank of second lieutenant and was sent to France to conduct historical research on the Marines.

In the 1920s and 1930s, Cooper wrote screenplays, including the narrative for the Frank Buck film Wild Cargo,short stories, novels, magazine articles, and popular non-fiction books. He published 30 books during his career. Most of his non-fiction work focused on two subjects — the circus and crime. He was Annie Oakley's first biographer. His books Here's to Crime (1937), Ten-Thousand Public Enemies (1935) and Designs in Scarlet (1939) championed the cause of the young Federal Bureau of Investigation and made the case that corrupt local governments and police forces permitted lawlessness to flourish in many parts of the United States.

Cooper's work was much admired by FBI Director J. Edgar Hoover, who once said he is "the best informed man on crime in the U. S." — even allowing Cooper access to FBI case files. Cooper is widely believed to have ghostwritten the book Persons in Hiding (1938) as well as a number of magazine articles for Hoover.

Cooper wrote extensively on the danger of illicit drugs, particularly marijuana. He collaborated with Federal Bureau of Narcotics Director Harry Anslinger on the article "Marijuana, Assassin of Youth," which originally appeared in The American Magazine in July 1937.

Some of Cooper's correspondence with Hoover is archived at the University of Alaska Anchorage Library.

On September 29, 1940, Cooper committed suicide by hanging himself in the closet of a hotel room in the Park Central Hotel in New York City. He left a note instructing that the cash in his clothing should be used to settle his hotel bill but giving no indication as to a motivation for his suicide. In his FBI file, there are letters to Hoover from two associates stating that Cooper did not commit suicide but was murdered.