As sometimes occurs, the origins of the Harrier breed are somewhat shrouded in mystery; various accounts exist regarding exactly how and when the dogs developed. The first known pack of actual Harriers existed in the year 1260, so everyone agrees that the breed is quite old. But where exactly did these dogs come from? One theory is that very early crossings between Bloodhounds, Basset Hounds and extinct Talbot Hounds resulted in these mysterious dogs. Another theory postulates other crosses: between the English Foxhound, the Greyhound and the Fox Terrier. The last theory, and the one which many people accept, is that these dogs were merely the "next size down" of the Foxhound and were developed by simply breeding down the latter.

While the first concrete mention of the breed dates to the 1200s, there have been mentions of breeds similar in appearance to the Harrier that date to ancient Greek times, roughly 400 years before Christ. Indeed, hare hunting was a popular "sport" even back then and men were known to keep packs of hunting dogs that would accompany them and aid them on the hunt. The dogs mentioned in the ancient Greek writings referring to hare hunting, though, cannot be conclusively determined to be Harrier hounds; most experts agree that the breed was developed in the British Isles to be a scenting pack hound.

All agree that the breed was initially developed to hunt hares and rabbits. This was done with the hunter moving alongside the dog, on foot, and so the first Harriers were slower, more calculating dogs, somewhat like Bloodhounds. With changes in the trends and demands of hunting, though, the Harrier hound was slightly modified. They became very fast hounds that had an incredible sense of smell and a great deal of endurance and stamina while on the hunt. These qualities allowed the breed to also excel in hunting foxes and, while hares and rabbits remained its specialty, the Harrier hound was also a favorite of the fox hunters; this proved to be useful to the maintenance of the breed, as fox hunting became all the rage. The dog was, and is, extremely courageous, following its prey across any terrain imaginable, into dens and in all weather conditions; it is also a very intelligent, cunning breed, outsmarting even the wiliest of foxes to hunt them down. They are virtually inexhaustible and stories abound of prey collapsing from exhaustion after being targeted by a pack of these super hounds.

Some people think that the dog's name derives from the fact that it hunts hares; this is most likely not true. The word "harrier" derives from "harier", the ancient Norman-Saxon word for "hound". While the breed is a wonderful dog and an excellent hunter, its popularity in both England and the US is less than soaring. It seems as if dogs like Beagles and Foxhounds are chosen over this breed; breed clubs in American are trying to promote the dog's image and familiarize the public with his qualities.