The Bullmastiff origin and history display a great example of a purpose-bred dog with a lineage that can be easily traced and understood. The Bullmastiff dog breed history originates from England and while its history is not as long and storied as other breeds, it is a close descendant of one of the oldest breed of dogs in England, the Mastiff. The Mastiff, a giant dog breed that descended from the Alaunt and the Molosser, is believed to have been introduced into ancient Britain more than 2000 years ago.

The Bullmastiff, however, was only introduced in about 1860 when the Mastiff was crossed with the Old English Bulldog. At this time, gamekeepers needed a dog to help protect their estates and flocks from game poachers, mostly poachers of deer from their estate. The Mastiff was apparently too slow and cumbersome for the job and the Bulldog was too small to be effective. The solution was a mix of about 60% Mastiff with 40% Bulldog, thus creating the Bullmastiff.

This new dog called the "Mastiff with a touch of bull" or more commonly Bullmastiff, was just what gamekeepers needed to watch their estates as his dark coat and quiet demeanor could surprise poachers, and then, rather than maul or kill the criminal, they would pin them to the ground without biting them. The Bullmastiff origin, then, arises from this practical application and was commonly called the "gamekeeper's night dog".

The Bullmastiff dog breed was used for some time as the gamekeeper's guard, however, eventually the Bullmastiff was used in other capacities, such as a sentry or guard dog as well as work with the army and police. The crossbreeding between the Mastiff and the Bulldog and the magic 60/40 mix, continued, but eventually a purebred line was formed. In 1924 some conformity was established in the Bullmastiff dog breed and it was recognized by the English Kennel Club in 1924.

The American Kennel Club later would recognize the breed in 1933. The dog was famously used to guard the DeBeer diamond mines in South Africa as well as John D. Rockefeller's New York estate in addition to being used in emergencies such as the one in Mau-Mau Uprising in Kenya.