The Canadian Kennel Club voted to fully recognize Glens in 2017 after the breed spent years on the Miscellaneous list; approval by Agriculture Canada is pending.

Reportedly, the Glen's history began during the reign of Elizabeth I, who hired French and Hessian mercenaries to put down a rebellion in Ireland.

[citation needed] Glens were originally used for eradicating other animals such as rat, fox, badger, and otter, and also as a general-purpose farm dog for herding and family companionship.

Unlike many other terriers, they are "strong dogs" rather than "sounders"—they were bred to work mute to ground, going silently into dens after their quarry rather than barking at it to alert their handlers.

Glens have a large head, with rose or half-prick ears; short, bowed legs; and a straight topline that rises slightly toward the tail.

The shoulders, chest, and hips are sturdy and muscular (the AKC breed standard specifies an impression of "maximum substance for size") and the front feet are turned out.

The breed is considered unrefined, with antique features that were common in early terriers but which have since fallen out of favor with fanciers and breeders.

The Glen of Imaal terrier does not molt or shed much, and needs to be brushed or combed every week or two to keep the soft coat in good condition and free of matting.

Historically, the breed's tail was typically docked to a length just sufficient to serve as a handhold for pulling the dog out of a badger hole.

A genetic test is available for progressive retinal atrophy (type crd3), a congenital disorder that gradually results in blindness beginning at about five years of age.

Because they are front-heavy and achondroplastic, young Glens are particularly susceptible to growth plate injuries that can significantly affect the development of front leg bones.

Owners are advised to discourage their Glens from jumping off sofas, chairs, and beds until at least a year of age and to consult a veterinarian at the first sign of limping.

By maturity, most Glens develop a robust prey drive and will readily go for vermin such as rats, so they need to be well-socialized with other animals when young—particularly with small household pets that they might mistake for quarry, such as cats and rabbits.

Although not typically strong swimmers due to their short legs and dense body, some Glens can work in water, and others have been trained to herd and drive sheep and cattle.