Union Gallery opened in 1994 after more than a decade of intense lobbying by Queen's University art students, with support from faculty and staff. Art on the Line (an Alma Mater Society sanctioned club) was formed in 1988 to petition for the inclusion of a designated gallery at Queen’s for student artists to exhibit their work and gain experiential professional development in the arts.

On April 5, 1990, the Alma Mater Society (AMS) Assembly ratified the AMS Capital Allocation Committee final report, which allocated $340,000 towards the construction of a student art gallery in Stauffer Library. UG officially opened its doors on October 6, 1994. With the gallery’s opening, Art on the Line was dissolved, and a new operating board was created, alongside the hire of Lynn Hunt as interim Gallery Manager. Jocelyn Purdie was hired in Fall 1994 as Managing Director, then Gallery Director, and retired in early 2020. Carina Magazzeni was hired as Gallery Director in February 2020. The Gallery Assistant position transitioned to a core professional staff position in August 2021 with the hire of Abby Nowakowski as Administrative & Communications Coordinator, promoted to Programs Director as a co-leadership structure in April 2022. UG officially incorporated as a not-for-profit organization on April 13, 2022. In September 2022, Morgan Wedderspoon took over the role of Gallery Director. While the gallery is connected and affiliated with Queen's University, UG remains independent with its own organizational profile, mandate, and Board of Directors.

Since its inception, Union Gallery has been a student-driven organization, with a blend of core professional and student staff and artists. UG’s integration of student and professional artistic programs remains unique in Canada.

UNION GALLERY is funded and supported by Queen's University, Alma Mater Society (AMS), Society of Graduate and Professional Students (SGPS), Ontario Arts Council, City of Kingston Arts Fund–Kingston Arts Council and the City of Kingston, with partnerships with Stauffer Library, Cultural Studies, Screen Cultures and Curatorial Studies, and Art History and Art Conservation.