Social support is one of the key factors that determines the success of protected areas. An ex-ante evaluation of the social support regarding the establishment process of protected areas could facilitate a more effective formation and hence improved management of such areas. Public backing for new parks could depend on several factors, including relationships with already established protected areas, changes in land ownership, changes in management actions, and potential impacts on the territory. We evaluated the support of local indigenous and non-indigenous communities for the creation of the new Patagonia Parks Network. This involves the donation of land by the Tompkins Conservation to the Chilean State, the second of which is committed to creating, expanding or reclassifying protected areas. We analyzed the renaming and reclassifying of the Alacalufes National Reserve to the Kawesqar National Park. We estimated local peoples' perceived costs and benefits and their support of (i) the donation process, (ii) the reclassification from reserve to park, and (iii) potential changes within the territory associated with new protected areas. The balance between the costs and benefits that people perceived of already established protected areas influenced their support for new ones. Although there is general social acceptation of the donation process and the establishment of parks among local people, indigenous communities may reject parks if their land-use requests for the park, including terrestrial and marine areas, are not included within the park's management plans. Partial rejection by Kawesqar representatives may inhibit the success of parks. Our ex-ante evaluation provides empirical evidence about underlying social factors related to the successful establishment of protected areas.