In this sub-alpine region the weather ranges from cold winter nights to warm summer days, and it can change very quickly. Snow normally falls on the Bimberi and Brindabella Ranges during winter, and is not uncommon throughout most of the park. The highest mountain is Bimberi Peak (1911 m) which is the highest peak in the Australian Capital Territory.
Namadgi is a local Aboriginal name for the mountains situated to the southwest of Canberra. Aboriginal presence in the area has been dated to at least 21,000 years. There are numerous Aboriginal sites in the park including paintings at Yankee Hat dating from at least 800 years ago. The area is one of cultural significance to indigenous Australian people of the Australian Alps region, and in particular the Ngambri, and the park's management plan is exercised with their consultation. In April 2001 representatives of the Ngambri communities entered into an agreement with the ACT government which recognised their traditional association with the park's lands and their role and duty to their ancestors and descendants as custodians of the area, and established a system of cooperative management.
The area has a European history dating back to the 1830s when settlers moved into the area and cleared the valleys for farming. The mountains and ridges remain forrested. Namadgi National Park was created in 1984.
The Visitor Centre is located 2 km south of Tharwa on the Boboyan-Naas Road.