The Tudor-style Mount Allison Memorial Library was opened on 8 June 1927, and dedicated to those Allisonians who lost their lives in World War One. President George J. Trueman chaired the event. The crowd that assembled were addressed by the Honorable W. F. Todd, Lieutenant-Governor of New Brunswick, and Rev. C. MacKinnon, Principal of Pine Hill Divinity Hall. The occasion concluded with the reading of the names of the war dead.
For the first time in Mount Allison’s eighty-four year history there was a building dedicated solely to library purposes. This allowed the consolidation of library holdings that had been scattered in a number of buildings around campus. The new $110,000 building was built to accommodate 60,000 volumes, providing the necessary room for growth. Staff consisted of faculty member Dr. F. W. W. DesBarres a cataloguer and two clerks. By 1940, DesBarres and his staff had increased the collection to 43,000 volumes. The Mary Mellish Archibald Memorial Library (MMAML), formerly in the Ladies’ College, had been assigned its own room, complete with oak furniture and sound equipment for the record collection. In the 1930s it was extended across a complete floor of the stacks. A ‘capacious vault’ was provided to provide a fireproof space for archival material. 
In 1942, Winifred Snider (BA, B.LSc. (Toronto), who had worked as Dr. DesBarres’ Assistant Librarian for nine years, was appointed as chief Librarian, the first professional librarian to hold this position at Mount Allison. When she left the position in 1945, changes were introduced and professor H. P. Gundy, after a summer session in Library Administration at Columbia University, was appointed Director of Library Services. Mary D. Falconer (1945 - 1949) served as Librarian, by which time the holdings had increased to 75,000 volumes. She was followed by Olga Bishop (1949 - 1953), and Laurie Allison (1953 - 1967).
As spacious as the new building had seemed when first occupied, the period of rapid expansion common to all universities after World War Two made an addition to the library necessary. The collection had grown to 120,000 volumes by the mid 1950s, archival material spilled over from the Vault into the Board Room, and staff had increased to ten persons. A 1950 student guide noted branch libraries – a library in the Science Building, the Carnegie Music Collection of eighty books in the office of the Dean of Music, and a library in the common room of the Academy.
An expansion was critically needed and plans set in motion. Construction of the Memorial Library’s new William Morley Tweedie Annex began during the fall of 1959. The Annex was designed by the architectural firm of C. A. Fowler & Co., and built by Parsons Construction Ltd., Moncton, NB.
Marion Ashe, who worked in the Circulation Department at the time, described the effect construction had on operations in the Memorial Library:
“…this meant all books from the different rooms downstairs and the furniture from the Mary Mellish reading room had to be moved to the main floor lobby. The end wall was removed, a bit of torture, with plaster dust, the deafening noise of drills, dampness and cold. At times we took inventory with snow boots and coats and perhaps gloves. The books there grew little fur coats from dampness; some looked like little kittens instead of books.” 
The William Morley Tweedie Annex opened on 13 August 1960, increasing the stack capacity of the building to 140,000 volumes. It was funded through a bequest from professor W. M. Tweedie and his sister Leora Tweedie and a grant from the Canada Council. The Annex provided only short-term relief and space issues quickly surfaced again because of the continued and accelerated growth of the University in the 1960s. In addition, the library was receiving large gifts of books, such as the collection of Acadiana donated by Winthrop Pickard Bell in 1965.
The official opening took place on 13 August 1960. Dr. N. T. Avard, Chair of the Board of Regents, presided. The speaker was Dr. David A. Jonah, Mount Allison graduate and Librarian at Brown University. Once the keys were presented, the ribbon cut by Dr. F. W. W. DesBarres, and the doors opened, tours were carried out for those assembled and a reception held in one of the new reading rooms. A display of songs, ballads and broadsides from the Mary Mellish Archibald collection was mounted in new cases.
Through a gift received from the Canada Council, Mount Allison commissioned artist Anne Kahane to design a sculpture that was placed on the building in 1961.
The compilers of the Mount Allison Faculty Association's 1962 Excellence Report  had calculated that at the current rate of acquisition, the Memorial Library would be full by 1967. They therefore recommended a further expansion to the building. A subsequent study determined that the site would not accommodate another addition and, besides, would not meet the requirements of a modern library.
In 1966, President Laurie Cragg described the radical conceptual changes in library architecture and services that had occurred since 1927:
"Gone is the concept of the baronial entrance hall, of the lofty spacious reading rooms, of the separated limited-access stacks; outmoded too is the idea that a library is solely a place to store and consult printed (or written) material. The modern library should make a variety of study materials – books, periodicals, documents, microfilm and micro-cards, maps, records, tapes, prints and reproductions – readily accessible to all its patrons. The books should be in open stacks with reading tables dispersed among them; there should be study carrels, faculty studies (sic), typing rooms, audio visual rooms, rare book rooms, browsing rooms – all the appointments that will make reading and study attractive and convenient." 
In 1966 preparations began for a new library building. Chief Librarian Eleanor Magee (1967-1979) assisted in its planning and was responsible for supervising the move to new quarters. When the Ralph Pickard Bell Library opened in October 1970, the Memorial Library building underwent significant renovations and became a University Centre for students and alumni.