Through his grandmother's persistence Brown was commissioned in 1857 "without purchase" as an 8th Regiment ensign.
Continuing across the prairie to Fort Garry, he was wounded by Blackfoot, then traded whisky in the Portage area. Employed briefly by a private company carrying mail for the US Army in the Dakota and Montana territories, Brown remained with
the military as a civilian "tripper." Despite capture and near death at the hands of Sitting Bull in
In 1877, at Fort Benton, Montana, Brown quarrelled with and killed Louis Ell, a celebrated hunter. Acquitted by a territorial jury he settled at Waterton Lakes, where he traded and established a reputation as guide and packer. During the 1885 North-West Resistance, he became chief scout for the Rocky Mountain Rangers.
Brown early foresaw the need to preserve the Waterton area and campaigned strenuously on its behalf. With the establishment of the Kootenay Forest Reserve in 1895 he became fishery officer and, in 1910, forest ranger. In 1914 his dream of further conservation was realized when the reserve became Waterton Lakes National Park, was enlarged and made contiguous with the international boundary and Glacier National Park in the US.