The Bullmastiff was specifically bred to bring down a man without biting him and hold him until his Master arrived. In the 1800s the estates of Great Britain suffered serious losses from "poaching" or the stealing of livestock and game and the Bullmastiff was bred to assist in eliminating poachers. This is a big dog, with a big attitude, but was not bred to attack but rather to hold at bay. The original cross of bull dogs with mastiffs produced this tractable yet powerful breed. The foundation stock was 50% Mastiff and 40% Bulldog. The common known term name for the breed early on was "The Game-keepers Night Dog". At first this was a rather generic description for all the big dogs that patrolled the estates but gradually these original dogs were more selectively bred and became what is today known as the Bullmastiff.

The Bullmastiff should have a large, square head with some wrinkling of the brow, a short broad muzzle with a slight upturn to the nostrils and a neck as broad and square as the head, on equally broad powerful shoulders. Unlike the Bulldog, the front legs should be straight. The chest should be deep and the back short, presenting a nearly square appearance to the body. The entire picture should be one of power and strength. The Bullmastiff is 24-27 inches at the withers, weighing between 110-130 pounds. The coat is short and dense, colors can be brindle, fawn, or red, with a black "mask" on the face. The Bullmastiff is somewhat shorter than a Mastiff and certainly stockier of build, a good Bullmastiff should be quite blocky in appearance, while a Mastiff is taller and rangier.

The Bullmastiff, like all large breeds, requires an owner with some knowledge of training and the willingness to socialize the puppy in its early life. As usual with any breed, a buyer who wishes to purchase a Bullmastiff puppy needs to be wary of irresponsible breeders who breed only for profit rather than a passion for the breed . The Bullmastiff is not for everyone, a neat housekeeper will not be happy with the amount of drool that the dog can put out. The coat is easy care and the general health is basically good, there being few genetic problems, except for hip dysplasia which is always an important consideration and care should be taken that x-rays are done before breeding.

The Bullmastiff is a powerful large dog with a fearsome look but is in truth a gentle and trustworthy dog. They are not excitable, actually being rather docile and gentle. They are loving to children and protective without being overly aggressive. The Bullmastiff possesses a delightful sense of humor and they can be quite "clownish" . This is a dog that is very easy to train, desiring nothing more than to please its owner. Perhaps because they were bred to hold a man at bay and not maul or kill, they have a sense of wisdom combined with their watchdog instincts and generally are quite intelligent and thoughtful in their response to strangers. They are good watchdogs and will accept strangers only when introduced properly by their masters and will seldom bite or attack, preferring to stand their ground and bark. This is a breed that is not excitable by nature and they do the business of guarding quite efficiently, since their size combined with their bark is quite sufficient to deter unwanted visitors. This is a dog that is great for country life or suburban areas but they should always be fenced or on a leash, even when on a farm or ranch. They are territorial by nature and will police the entire property that they have access to.