In 1894, workers constructed what became Old Main from locally quarried Moenkopi sandstone on land purchased from the railroad. Although the Territorial Legislature intended it for a reform school, locals wanted an educational institution. In response, Flagstaff legislator Henry Ashurst introduced a bill creating the Northern Arizona Normal School (NANS), which held its first classes on September 11, 1899.
NANS initially offered four years of high school with additional teacher training. From 1899 to 1905, Main Hall served as the School's only building and contained an assembly room, library, classrooms, recitation rooms, offices, and a practice teaching area. Interest in NANS grew slowly from twenty-three students and two faculty in 1899 to seven teachers and fifty-four enrolled in 1905. Annual tuition then averaged just $20 with total student expenses coming to $190.
Renovations in 1928 remodeled classrooms and added a library reading room. From 1961 to 1984, Old Main served as a men's dormitory for Arizona State College, after President J. Lawrence Walkup suggested it could provide needed housing while resident fees financed necessary repairs. Following the departure of the last student residents, Northern Arizona University converted the space into temporary offices. In 1989, the University began a twenty-one month remodeling project, turning the historic structure into an art gallery, museum, and administrative offices. Additional work in 2009 repaired roofs and walls and a 2013 landscaping project revitalized its grounds. Today, Old Main is the best preserved example of Richardsonian Romanesque architecture in northern Arizona.