The Mastiff name probably evolved from the Anglo-Saxon word "masty", meaning "powerful". The Mastiff is descended from the ancient Alaunt and Molosser and is recognized as the oldest British breed. The Mastiff might have been brought to Britain in the 6th century BC. It was used in the blood sports of bear-baiting, bull-baiting, dog fighting, and lion-baiting. Throughout its long history, the Mastiff has contributed to the development of a number of dog breeds.

When Sir Peers Legh was wounded in the Battle of Agincourt, his Mastiff stood over and protected him for many hours through the battle. Although Legh later died, the Mastiff returned to Legh's home and was the foundation of the Lyme Hall Mastiffs. Five centuries later this pedigree figured prominently in founding the modern breed.1

Some evidence exists that the Mastiff came to America on the Mayflower, but the breed's documented entry to America did not occur until the late 1800s.

In 1835, Britain passed legislation making baiting illegal. Subsequently, the Mastiff lost popularity and was virtually decimated in England by the Second World War; however, sufficient numbers had been brought to America by that time to keep the breed going. Since that time, it has gradually risen in popularity.