By the end of the 18th century, the English Classic races had been established. These are the St. Leger Stakes, founded in 1776, the Epsom Oaks, founded in 1779, and the Epsom Derby in 1780. The distances of these races, ranging from 1 mile (1.6 km) to 1.75 miles (2.82 km), led to a change in breeding practices, as breeders concentrated on producing horses that could race at a younger age than in the past and that had more speed. In the early 18th century, the emphasis had been on longer races, up to 4 miles (6.4 km), that were run in multiple heats. The older style of race favored older horses, but with the change in distances, younger horses became preferred.

Selective breeding for speed and racing ability led to improvements in the size of horses and winning times by the middle of the 19th century. An aspect of the modern British breeding establishment is that they breed not only for flat racing, but also for steeplechasing.

Thoroughbreds are often known for being either distance runners or sprinters, and their conformation usually reflects what they have been bred to do. Sprinters are usually well muscled, while stayers, or distance runners, tend to be smaller and slimmer. Historically, Thoroughbreds have steadily increased in size: the average height of a Thoroughbred in 1700 was about 13.3 hands high. By 1876 this had increased to 15.3.

In addition to racing, Thoroughbreds compete in eventing, show jumping and dressage at the highest levels of international competition, including the Olympics. They are also used as show hunters, steeplechasers, and in western riding speed events such as barrel racing. Mounted police divisions employ them in non-competitive work, and recreational riders also use them. Thoroughbreds are one of the most common breeds for use in polo in the United States. They are often seen in the fox hunting field as well.