Daniels graduated from college in Milford, Connecticut, and became a specialist in the metal industry. From 1958 to 1972, he was editor of the magazine Metalworking. In the 1950s, he published numerous short stories, and in 1956 he published his first novel, In His Blood, nominated for the Edgar Allan Poe Award.

Little known in France, Harold Robert Daniels, however, writes Claude Mesplède and Jean-Jacques Schleret "remarkable works for the quality of the realistic plot and description of the small towns of the United States". His fourth novel, The Snatch, published in 1958, is described by John D. MacDonald as "one of the modern classics of crime and punishment. His sixth and last novel, published in 1966, House On Greenapple Road, is appreciated by Claude Mesplède as "undoubtedly his most complete book" and adapted for television in 1970. One of his new Death does not wait (Road Hog) is adapted twice in each of the two series Alfred Hitchcock presents.