The total area of the botanical garden is 147 acres (0.59 km2), at 460 meters above sea level, and with a 200-day annual rainfall. It is managed by the Department of National Botanic Gardens, Sri Lanka.
The history of the Royal Botanic Gardens dates as far back as 1371 when King Wickramabahu iii ascended the throne and kept court at Peradeniya near Mahaweli Ganga. Later, in the reign of King Kirti Sri from 1747 to 1780 this was made a Royal Garden and from 1780— 1798 King Rajadhi Rajasirighe resided therein, where a temporary residence was erected for him.
A vihare and dagoba were built in the reign of King Wimala Dharma which was improved by King Rajadhi Rajasinghe. The vihare and dagoba were destroyed by the English when they occupied Kandy. The famous historical battle of Gannoruwa between Rajasinghe ii and the Portuguese was fought on the Northern side of the river. A priest resided here till the Gardens were formed by Mr. Alexandar Moon in 1821 six years after the final conquest of the Kandyan Kingdom.
In 1810 under the advice of Sir Joseph Banks a garden named Kew was opened in Slave island and Mr. William Kerr was appointed as its Superintendent. In 1813 the garden was moved to Kalutara for the reception of economic plants which could be cultivated there on a larger scale than was possible at Slave Island. Kerr died in 1814 and under the rule of his successor Mr. Alexander Moon this Garden was finally moved to Peradeniya in 1821 as it was found to be favourable and better adapted for the proposed Botanic establishment. The transfer of exotics from the Kalutara Garden was made by successive Superintendents at least up to 1843.