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.

With little formal education, at age 17 he began publishing plant collections and in 1884 he and his wife, Dr. Carrie E (Marvin) Leiberg (1852-1936), settled in the Lake Pend Oreille, Idaho Territory.

He worked as a field botanist for Frederick Vernon Coville (1867–1937), curator of the United States National Herbarium.

[3][4] Leiberg contributed to and authored many publications including The Bitterroot Forest Reserve (U.S. Geological survey.

[6][7] Leiberg left government service in 1906 and briefly settled on a farm near Leaburg on the McKenzie River east of Eugene in Lane County, Oregon.