The site of the garden is part of the first land grant made at Mount Tomah in 1836.  After various changes in ownership, in 1934 a portion of this land was sold to Mrs. Effie Brunet, who with her husband, the French born Alfred Louis Brunet, established a farm for the production of cool climate flowers.

Following Mr Brunet's death, Mrs Brunet gave the property to the NSW Government in 1970 as a cool climate annex of the Royal Sydney Botanic Gardens.  There are in excess of 34,500 plants in the garden which covers 28 hectares of cultivation, in which the oldest tree is over 400 years old. 

There are 125 different species of birds on Mount Tomah . 

The garden is open all year round, and is an ideal picnic location.