The Sealyham Terrier was named by its original breeder, Captain Edwardes, after his mansion, Sealyham, near the Sealy river in Pembrokeshire, South Wales.

Captain Edwardes is thought to have begun developing the Sealyham Terrier around the year 1860. As an avid sportsman he desired a dog to work with his hunting pack of Otterhounds and go to ground after badger. This required a dog with great courage, stamina, and agility and a white colour so that the hounds and sportsman involved in the hunt would not mistake the Sealyham for the prey.

The Sealyhams were not required to kill the badger, but to keep it in one place and to bark to signal the huntsmen of the badger's location underground so that they could dig into the den.

Although there is no complete record of the breeds used by Captain Edwardes to develop the Sealyham Terrier, the Welsh Corgi, White Bull Terrier, Dandie Dinmont Terrier, Wire Fox Terrier and West Highland White Terrier are all thought to have played a role.

Although a rare breed today, during the 1920s and 1930s the breed enjoyed popularity and was owned by Gary Cooper, Cary Grant, Humphrey Bogart, Richard Burton and Alfred Hitchcock — whose own Sealyhams can be seen in his films The Birds and Suspicion. Sealyhams also were a popular subject for postcard artists during this period.

The Sealyham is a double-coated breed with a soft undercoat and a harsh, weather-resistant outer coat which requires regular maintenance.

For the show ring, the Sealyham is hand stripped — the long and dead hairs are plucked out by hand. The stripping process is time-consuming but the coat of a Sealyham kept just as a companion can be clipped. The luxurious furnishings on the head, legs and chest require regular brushing to eliminate knots and tangles.

The clown of terriers, the Sealyham is a loyal, intelligent, sometimes stubborn but always devoted companion, and although most terriers are busy dogs, the Sealyham is the couch potato of the Terrier world, having a much more relaxed attitude.

The Sealyham is a large dog in a small package and makes an ideal companion for both city and country living.

A moderate amount of exercise will keep him healthy and happy.