Sterling was born in Queens, New York. She earned a bachelor's degree in economics at Brooklyn College, worked as a union organizer, and was briefly member of the Young Communist League. After receiving a master's degree in journalism from Columbia University in 1945, she became the Rome correspondent of "a fly-by-night American news agency." When it folded, she joined The Reporter, which she wrote for until it ceased publication in 1968. Sterling began writing her first book after losing her job at The Reporter; it was published in 1969. She also wrote for various newspapers and magazines, including The New York Times, Washington Post and Reader's Digest.

She married Thomas Sterling, a novelist, in 1951. After spending their honeymoon in Italy the two moved there, living in Rome for several decades. They had two children. She died of cancer at age 75, in a hospital in Arezzo.

Sterling's first book revisited the 1948 death of Jan Masaryk, the Czechoslovak foreign minister, which she blamed on Soviet or Czechoslovak Stalinists. More controversial were her books The Terror Network (1981) and The Time of the Assassins (1984). In the former book, which was translated into 22 languages, she claimed that Soviet Union was a major source of backing behind terrorist groupings around the world. The book was read and appreciated by Alexander Haig and William Casey, but its arguments were dismissed by the CIA's Soviet analysts. Sterling was the first to claim (in a September 1982 article in Reader's Digest) that the 1981 assassination attempt on Pope John II had been ordered by the Bulgarian Secret Service, a theory that became known as the "Bulgarian Connection." The Time of the Assassins dealt with the assassination attempt and advanced this theory. Her last two books dealt with the Sicilian Mafia and post-Communist globalized organized crime, respectively.