The Manchester Terrier is a breed of dog of the smooth-haired terrier type. It was first bred in the 19th century to control vermin, notably rats, at which it excelled. So efficient at the task was it that it often appeared in rat-baiting pits until that sport, which had effectively been illegal in the UK since 1835, finally died out at the beginning of the 20th century.

The breed is generally healthy, although dogs can be affected by several inheritable genetic disorders. A crash in the number of registered Manchester Terriers following the Second World War has resulted in the Kennel Club categorising it as a vulnerable native breed, in danger of extinction.

The Manchester Terrier was developed from the Black and Tan Terrier and the Whippet.. Writing in the early 16th century, John Caius describes a Manchester-terrier type of dog in De Canibus Britannicis, and at the beginning of the 19th century Sydenham Edwards described what he called a Manchester Terrier in his Cynographia Britannica.

The Black and Tan Terrier had an almost legendary status as a rat killer, an ability that was much prized in overcrowded and rat-infested cities such as 19th-century Manchester. The sport of rat baiting, in which a terrier was thrown into an enclosure filled with rats, and timed to see how long it took the dog to kill them all, had become popular by the early 19th century along with rabbit coursing. In an effort to produce a dog that could excel at both sports, the breeder John Hulme decided to cross a Black and Tan Terrier with a Whippet. Similar dogs were bred in various other parts of England, but by 1860 Manchester had become the breed centre for these new terriers, and so they became known as Manchester Terriers. Other breeds, including the Italian Greyhound and the Dachshund, may also have been introduced into the bloodline.

The Manchester Terrier gained the nickname of the Gentleman's Terrier in Victorian times, because of its dignified demeanour.

By the early 19th century a closer facsimile to the current Manchester terrier had evolved. In The Dog in Health and Disease by J. A. Walsh, a full chapter was devoted to the black and tan, for the first time recognising it as an established breed. The description given by Walsh is still relevant: Smooth haired, long tapering nose, narrow flat skull, eyes small and bright, chest rather deep than wide, only true colour black and tan.

Some terrier breeds have a reputation for being "stoic and dour", but such terms do not apply to the intelligent and inquisitive Manchester Terrier, who is as "feisty and affectionate" as he is "courageous and tough", and makes a "loyal, eager-to-please" companion.

The Canadian and American Kennel Clubs recognise two varieties of Manchester Terrier, the original and a miniaturised variant, the Toy Manchester Terrier. The latter was recognised as a separate breed by the American Kennel Club in 1938, and is still considered to be a separate breed by the British Kennel Club, the English Toy Terrier (Black & Tan). Where the Manchester Terrier may have button ears, erect ears, or cropped ears, the Toy Manchester Terrier only has erect ears. Other than the size difference and ear type, the Manchester Terrier and the Toy Manchester Terrier have the same overall appearance. Since 1958 the American Kennel Club has considered both to be varieties of the same breed.