It is thought that the toy spaniels that eventually became the King Charles Spaniel originated in the Far East, primarily Japan. They may share a common ancestry with the Pekingese and Japanese Chin. Toy spaniels were given as gifts to European royalty.
In the 17th century, toy spaniels began to feature in paintings by Dutch artists such as Caspar Netscher and Peter Paul Rubens. Spanish artists, including Juan de Valdés Leal and Diego Velázquez, also depicted them; in the Spanish works, the dogs were tricolour, black and white or entirely white. French naturalist Georges-Louis Leclerc, Comte de Buffon would later describe these types of dogs as crosses between spaniels and Pugs.
Toy spaniels continued to be popular in the British court during the reign of King James II, through that of Queen Anne. Popular types included those of the white and red variety. Following the Glorious Revolution in 1688 and the reign of King William III and Queen Mary II, the Pug was introduced into Britain which would eventually lead to drastic physical changes to the King Charles Spaniel. Comparisons between needlework pictures of English toy spaniels and the continental variety show that changes had already begun to take place in the English types by 1736, with a shorter nose being featured and the breed overall moving away from the one seen in earlier works by Anthony van Dyck during the 17th century.
The varieties of toy spaniel were occasionally used in hunting, as the Sportsman's Repository reported in 1830 of the Blenheim Spaniel: "Twenty years ago, His Grace the Duke of Marlborough was reputed to possess the smallest and best breed of cockers in Britain; they were invariably red–and–white, with very long ears, short noses, and black eyes." During this period, the term "cocker" was not used to describe a Cocker Spaniel, but rather a type of small spaniel used to hunt woodcock. The Duke's residence, Blenheim Palace, gave its name to the Blenheim Spaniel. The Sportsman's Repository explains that toy spaniels are able to hunt, albeit not for a full day or in difficult terrain: "The very delicate and small, or 'carpet spaniels,' have exquisite nose, and will hunt truly and pleasantly, but are neither fit for a long day or thorny covert." This idea was supported by Vero Shaw in his 1881 work The Illustrated Book of the Dog, and by Thomas Brown in 1829 who wrote, "He is seldom used for field–sports, from his diminutive size, being easily tired, and is too short in the legs to get through swampy ground." During the 19th century, the Maltese was still considered to be a type of spaniel, and thought to be the parent breed of toy spaniels, including both the King Charles and Blenheim varieties.
In 1903, the Kennel Club attempted to amalgamate the King James (black and tan), Prince Charles (tricolour), Blenheim and Ruby spaniels into a single breed called the Toy Spaniel. The Toy Spaniel Club, which oversaw those separate breeds, strongly objected, and the argument was only resolved following the intervention of King Edward VII, who made it clear that he preferred the name "King Charles Spaniel". In 1904, the American Kennel Club followed suit, combining the four breeds into a single breed known as the English Toy Spaniel. The Japanese Spaniel was also considered a type of toy spaniel, but was not merged into the new breed and was recognised as a breed in its own right.