The herbarium was founded in the 1890s on the collections of Charles Piper and his students. Piper was on the faculty at Washington State College (now Washington State University) from 1893 to 1903. The herbarium collection, especially Piper's own contributions and those of William Cusick and Wilhelm Suksdorf, served as the basis of Piper's Flora of the State of Washington (1906). Piper and R. Kent Beattie, who was also on the faculty at the State College of Washington from 1903-1912, used the herbarium collection in the preparation of their Flora of the Palouse Region (1901), Flora of Southeastern Washington and Adjacent Idaho (1914), and Flora of the Northwest Coast (1915).
In the years following the active collecting and preparation of floras by Piper and Beattie, little systematics research was centered in the herbarium. During this period, however, about 6,000 of William Cusick's collections were purchased for the herbarium. Cusick in 1913 sold the bulk of his original collections to Oregon State University. His second major set of collections, which centered on the Wallowa and Blue Mountains, are in the Marion Ownbey Herbarium.
The next major phase in the herbarium began with the arrival of Harold St. John from Harvard in 1920. St. John was an avid plant collector and added 14,000 specimens to the herbarium while he was at Washington State College. He was interested particularly in discovering new entities and added 123 types to the herbarium collection. The herbarium benefitted from St. John's scholarship. He developed the herbarium library so that it could serve in taxonomic research. From the early 1920s, St. John aimed to revise Piper and Beattie's Flora of Southeastern Washington and Adjacent Idaho. Although St. John left the college in 1929, the herbarium and his collecting in the area served in his Flora of Southeastern Washington, which was published in 1936.
The herbarium grew dramatically in 1932 from Wilhelm Suksdorf's bequest of his 30,000 specimen herbarium to Washington State College. Suksdorf collected widely in the Pacific Northwest after his college education at Grinnell College and the University of California at Berkeley. This period of collecting extended from 1876 to 1887. In 1887, Suksdorf went to Harvard to become Asa Gray's assistant in the herbarium. Following Gray's death in 1888, Suksdorf returned to Washington and continued collecting in the Pacific Northwest. He made his livelihood during this time by selling plant specimens and seeds.
Lincoln Constance served as director of the herbarium from 1934 to 1937. Constance strived to curate the Suksdorf specimens and a large backlog of collections left from the St. John era. During Constance's tenure as director, the herbarium was moved from the basement of Humphrey Hall to the New Science Hall. After leaving Pullman, Lincoln Constance became renowned for his systematic research at the University of California at Berkeley. Following the departure of Constance, Carl Sharsmith worked as an instructor of botany and curator of the herbarium from 1937 to 1939. Sharsmith's time in the herbarium was noted for the emphasis he gave to accessioning acquisitions from Charles Piper's private herbarium. After leaving Pullman, Sharsmith became a well known ranger and botanist in the Sierra Nevada of California.
Marion Ownbey came to Washington State College in 1939 and served as the director of the herbarium until his death in 1974. The herbarium expanded greatly under Ownbey's direction. It had housed about 90,000 specimens in 1939 but enlarged to 273,000 by Ownbey's death in 1974. Ownbey's research emphasized the monographic and biosystematic themes that reigned in the field during his era. This work centered on a monograph of Calochortus, revisionary studies of Allium and Castilleja, and a series of experimental investigations of hybrid speciation in Tragopogon. The Tragopogon research became a classic example of hybrid speciation and has been followed-up subsequently by the WSU systematists Doug and Pam Soltis and their students. Ownbey also contributed to the major floristic treatments of the Pacific Northwest, including Vascular Plants of the Pacific Northwest (by C. L. Hitchcock, A. Cronquist, M. Ownbey, and J. W. Thompson) and R. Davis's Flora of Idaho. Ownbey trained numerous graduate students, some of whom conducted monographic studies although others worked on the Florula Suksdorfiana project that aimed to curate Suksdorf's collections and identify more precisely through additional fieldwork their collection localities. The herbarium moved twice during Ownbey's tenure as director. In 1952, it was moved to Holland Library and then, in the 1960s, to its present location on the ground floor of Heald Hall. Marion Ownbey's distinctive research in plant systematics and his long term devotion to the development of the herbarium led the University to name the facility after him shortly before his death in 1974.
Amy Jean Gilmartin came to Washington State University in 1975 and served as director of the Marion Ownbey Herbarium until her death in 1989. The herbarium under her direction made use of new technologies. Gilmartin received a grant from the National Science Foundation to install a compactor system, which permitted the expansion of the herbarium collection without requiring additional building space. As an early advocate of the use of computer technologies in systematics, Gilmartin installed in 1976 a computer system in the herbarium that could be used for record-keeping and label-making. The collection expanded in new directions under Gilmartin's direction. Her interest and fieldwork in the tropics led to the acquisition of plants from those region s. Gilmartin's research emphasized Bromeliaceae and the herbarium acquired a significant bromeliad collection during her tenure as director. Following Gilmartin's death, the University entered a period of financial retrenchment. This ultimately led to the loss of the full-time curator's position, held at that time by Joy Mastrogiuseppe. Mastrogiuseppe's research on Carex led the herbarium to become a significant resource on the genus.
Larry Hufford became the director of the herbarium in 1993. Since that time the herbarium collection has grown significantly through the incorporation of the Walla Walla College Herbarium. The Walla Walla collection was acquired in the interim following Gilmartin's death, and curation and accessioning of the specimens began in earnest in 1994 and was completed in 1996. The incorporation of the Walla Walla College Herbarium added over 20,000 specimens to the Ownbey Herbarium. These specimens were collected primarily by Albert Grable and most were from eastern Washington. Grable traveled widely, however, and in addition to plants from the Pacific Northwest his specimens came from various locations in North America and the neotropics. The acquisition of Grable's Walla Walla College Herbarium is second only to the Suksdorf bequest in size among single gifts of specimens that the herbarium has received. A bequest from Betty Higinbotham of several thousand bryophytes was also obtained in the interim following Gilmartin's death. Under Hufford's direction, the herbarium expanded its specimen exchange program, especially emphasizing the taxonomic diversification of the Ownbey Herbarium through the acquisition of plants from outside of North America. Hufford retired in the summer of 2020 to move to Missoula, Montana.
Eric H. Roalson has been the director from 2020 to the present, and has overseen a number of initiatives, including the incorporation of the WSU-Tri-Cities / PNNL herbarium, move of the herbarium to new space in another building on campus (the Owen Science Library), and the hiring of the collections manager Walter Fertig in 2022. Other major initiatives ongoing are creating an annotated bryophyte checklist for Washington, several local floristic treatments, and the imaging and databasing of the rest of the collection.