The origin of Muay Thai is unclear at best. Many theories exist, however a popular on is that it was with the Tai people before the Tai immigration to Southeast Asia from China. Another is that it was adopted and modified off of Khmer martial arts when Thai culture was influenced by Khmer culture. A third theory is that a little bit of both the first and second theory occurred. Muay Thai evolved from its ancestor Muay Boran an unarmed combat used by Siamese soldiers in conjunction with Krabi Krabong.

As well as continuing to function as a practical fighting technique for use in actual warfare, Muay Thai became a sport in which the opponents fought in front of spectators who went to watch for entertainment. This kind of muay contests gradually became an integral part of local festivals and celebrations, especially those held at temples. It was even used as entertainment to kings.  Muay Thai is an art of self defense using the 8 main weapons of the body.  The 8 main weapons are the foot, knee, elbow, and fist on each side.  It is based on the principle of "doing no more than necessary to teach a lesson," it is equally well suited to be used as a competitive sport or as a self defense system.  In ancient times, Thai warriors had intensive training in the art, giving them a distinct advantage in close-combat situations. Royalty, military leaders, and even the common man regularly trained in Muay Thai.

The best known and most celebrated of the early fighting greats was Nai Khanom Otom , who, after been captured by the Burmese, regained his freedom by defeating twelve of the enemy's gladiators in an unarmed contest witnessed by the Burmese king.   Every stadium in Thailand honor the hero by dedicating one fight per year to him.

Muay gradually became a possible means of personal advancement as the nobility increasingly esteemed skillful practitioners of the art and invited selected fighters to come to live in the Royal palace to teach muay to the staff of the royal household, soldiers, princes or the king's personal guards.  Muay Thai became part of the military training during the reign of King Naresun the Great (1590-1605). He also practiced the art, and in doing so became a national hero.

King Chulalongkorn ascended to the throne in 1868 ushered in a Golden Age for Muay Thai.. Muay Thai progressed greatly during the reign of Rama V as a direct result of the king's personal interest in the art. The country was at peace and Muay Thaiy functioned as a means of physical exercise, self-defense, recreation, and personal advancement.  Masters of the art such as former fighters or soldiers began teaching Muay Thai  in training camps where students were provided with food and shelter. Trainees would be treated as one family and it was customary for students to adopt the camp's name as their own surname.

After the occurrence of a death in the ring, King Rama the VII pushed for codified rules for Muay Thai, and they were put into place. Before this fighters wrapped their hands in rope soaked in glue before being tied to the boxer's hands. According to legend there were some matches where ground glass was mixed with the glue. There were no such arrangements as weight divisions or three-minute rounds. A bout lasted as long as a fighter could continue. Many boxers lost their lives in the ring.  The new rules included the rules that the fighters should wear modern gloves and cotton coverlets over the feet and ankles. It was also around this time in the 1920s that the term Muay Thai became commonly used while the older form of the style was referred to as Muay Boran.

Most Thai boxers start training at the age of 7 years old.  They learn to use their legs, fists, knees, and elbows and are usually in the ring by their eleventh birthday.  The average Thai fighter retires during his middle or late twenties. After leaving the ring many will enter the monkhood for a short time. Most return later to their camps after to train or become trainers.