The original inhabitants of Sikkim were the Lepchas, which means "ravine folk." They came to the area from the direction of Assam and Burma. From the 1200's, the Bhutia, a Tibetan people, moved into the area. They included the Namgyal clan, who arrived in the 1400's and gradually won political control over Sikkim. In 1642, Phuntsog Namgyal (1604-1670) became the chogyal (king). He presided over a social system based on Tibetan Lamaistic Buddhism. His descendants ruled Sikkim for more than 330 years.

During the 1700's, Sikkim suffered invasions from Nepal and Bhutan, and lost much territory as a result. Nepalese also migrated to Sikkim and settled there as farmers. By the 1800's, Sikkim's population was ethnically very mixed, and internal conflict resulted. In 1814-1815, Sikkim assisted the British in a successful war against Nepal, and won back some of its lands.

In 1835, the British East India Company purchased the health resort of Darjeeling from Sikkim. During the mid-1800's, Sikkim violently resisted attempts to bring it under British rule, but in 1861 it finally became a British protectorate. The British had access through Sikkim to Tibet, and Sikkim's independent status was recognized.

In 1890, Britain and China signed a convention recognizing the border between Sikkim and Tibet. Later, the British installed a political official to help the chogyal of Sikkim run the internal and external affairs of the kingdom.

The Indian government took over responsibility for Sikkim's external affairs, defence, and communication in 1950. The struggle that had brought Indian independence in 1947 promoted a democratic upsurge in Sikkim. The chogyals lost their power as a result of the gradual introduction of a new democratic constitution. In 1973, India took Sikkim into the union as an associate member. In 1975, Sikkim became India's 22nd state.