Leiberg came to the United States in 1868 and settled near Lake Coeur d"Alene, Idaho. He spent the first part of his career as an explorer and plant collector for various flora projects mainly in Idaho, Washington, Oregon, and Nevada. Later he worked with the United States Geological Survey.
He supplied specimens to the New York Botanical Garden and in 1892 he spent the winter in Hamilton, Montana.
He worked as a field botanist for Frederic Coville, curator of the United States National Herbarium and in 1897 he was transferred to the United States Geological Survey and assigned to examine the area of the 6,480 square miles (16,800 km2) Bitterroot Forest Reserve which later became National Forests in Montana and Idaho. (The reserves had been expanded by President Grover Cleveland by his February 22, 1897 proclamation) He surveyed the Bitterroot reserve in 1897 and 1898 and wrote the 19th and 20th annual reports for the United States Geological Survey describing the topography, trees and mapping locations in an area previously relatively undocumented.
From 1900 to 1904 he published descriptions of several other western forest reserves. He spent a short time in the Philippines, a United States protectorate, where he was a forest inspector for the Insular Forest Service.
He left government service in 1906 and briefly settled on a farm in Eugene, Oregon.
He travelled the world in 1910 and died in 1913. He contributed to and authored many publications including Contributions to the Flora of Idaho and Minnesota and many forestry related works. sa
A number of plant species have the epitaph "leibergii" in his honor. Nymphaea leibergii