The early history of the Smooth Collie, like that of many dog breeds, is largely a matter of speculation. The most common view of the breed is that they are descended from a population of shepherds' dogs brought to Britain by the Romans around the 5th century. Even the origin of the breed's name is unclear, variously claimed to describe the early shepherd dog's dark color ("coaly"), or derived from the name of a breed of sheep once commonly kept in Scotland ("Colley").

The modern history of both the Smooth and Rough Collie began in the reign of Queen Victoria, who became interested in the shepherds' dogs while at Balmoral Castle in Scotland. In 1860, she purchased some of the dogs for her own kennel. With the Queen's interest, it became fashionable to own Collies. Thus began the breed's transformation from working farm dog, similar to the modern Border collie, to the largely pet and show dog we know today.

The Smooth Collie today is considered a variety of the same breed as the Rough Collie in countries such as the United States and Canada. The smooth and rough are classified as separate breeds in others, such as the United Kingdom and Australia. The latter is a fairly recent development, however, with the Kennel Club (UK) allowing the interbreeding of the two varieties until 1993.

The Smooth Collie is a medium to large dog, ranging in size from 20-26 inches at the shoulder and weighing 40-75 pounds. Standard size for the breed is on the larger end of the range in the United States and Canada, smaller elsewhere; for example, for the AKC, the range is 22 to 26 inches (56-66 cm) and 50 to 75 pounds (22.5-34 kg). In all standards, females should be significantly smaller than males. The Smooth Collie is slightly longer than it is tall, with a level back and a deep chest. The features of the head, particularly the "sweet" expression, are considered very important in the show ring. The breed has a long muzzle, flat skull, and semi-erect ears (although, in practice, the ears typically must be folded over and taped in puppyhood, or they will be fully upright in the adult dog).

The coat consists of a soft, extremely dense undercoat and straight, harsh outer guard hairs. The guard hairs are one to two inches long, with the longer hair mainly in a ruff around the neck and on the backs of the thighs. The coat requires a thorough weekly brushing. Shedding is moderate most of the year, heavy during the twice-yearly shedding season.

Smooth Collies come in four colors, three of which are considered acceptable by all standards worldwide. The universally accepted colors are sable (Lassie's color; can be light gold to deep mahogany), tricolor (mainly black with tan markings), and blue merle (silvery gray marbled with black), all marked with white areas on the chest, neck, feet/legs, and tail tip. Kennel clubs in the United States and Canada also accept white, sometimes called color-headed white. These Collies are predominantly white, with heads (and usually a body spot) of one of the other three colors.

The Smooth Collie is generally a sociable, easily trained family dog. Although not an aggressive breed, they are alert and vocal, making them both good watchdogs if well trained and potential nuisances if allowed to bark indiscriminately. Training this breed requires a light touch, as they are sensitive to correction and will balk at harsh treatment. They usually get along well with children and other animals. Smooth Collies tend to have retained more herding instincts than the rough variety, and have noticeably higher energy levels.

Smooth collies are used both as family pets and in obedience competition, agility, herding trials, and other dog sports. Some are still used as working sheepdogs. They are also useful as service animals for the disabled, and are being trained in some instances as guide dogs for the blind.

The Smooth Collie is a long-lived breed for its size, usually living 12 to 14 years. Like all dog breeds, they are susceptible to certain inherited or partially inherited health problems. Those problems currently include:

• Collie eye anomaly (CEA): A collection of eye problems ranging from minor blood vessel abnormalities to blind spots to severely deformed or detached retinas. This problem is so widespread in collies that completely unaffected dogs (called "normal eyed") are uncommon, although conscientious breeders have been able to gradually increase the normal population. The problem and its extent can be determined through an eye exam conducted before six weeks of age, and does not get worse over time. Mildly affected dogs suffer no impairments, and are fine pets or working dogs.
• Progressive retinal atrophy: Gradual degeneration of the retinas of the eyes, eventually leading to blindness. This disease is less common than CEA in Collies, but more difficult to breed away from, as symptoms are not usually detectable until the affected dog is middle-aged or older.
• Multidrug sensitivity: Sometimes fatal reactions to a class of common drugs, particularly ivermectin, used as a heartworm preventative and treatment for mites. The gene that causes this sensitivity has recently been identified, and a dog's susceptibility can now be determined through a simple blood test.
• Gastric torsion ("Bloat"): A painful and often fatal twisting of the stomach occurring in large or deep-chested breeds. Bloat can usually be prevented by feeding small meals and not allowing vigorous exercise immediately before or after eating.
• Epilepsy: Seizures of unknown origin. Frequency of the seizures can often be significantly reduced through medication, but there is no cure for this disease.