Alexandra "Sandy" Mason was born to Herbert E. and Anna E. Thorndike Mason in Greenfield, Massachusetts in 1931. Mason went on to study at Mount Holyoke College, where she first met her lifelong companion, Ann Hyde. Mason graduated from Mount Holyoke with a Bachelor of Arts in Greek in 1952. She then earned a Master of Library Science in 1955 from the Carnegie Library School. After obtaining her degree, Mason completed post-graduate work at Durham University and the Bodleian Library at Oxford University. Upon graduation, Mason worked as a reference librarian for the World Book Encyclopedia in Chicago until moving to Lawrence, Kansas a year later in 1957.

Mason started as a Special Collections cataloger at the University of Kansas, and along with visiting professor Bertram Colgrave and Ann Hyde, discovered and deciphered leaves from two different 11th century Anglo-Saxon manuscripts used as padding in a 17th century book's binding. One of her earliest contributions to the Spencer Research Library, Mason would go on to play a significant role in building renowned collections at KU and the Spencer Research Library.

Mason became the head of Special Collections at KU in 1963, later becoming the Spencer Librarian at the Kenneth Spencer Research Library on KU's campus after the new research library was built in 1968. During her long career at KU, Mason was an inductee in the University of Kansas Women's Hall of Fame in 1980 and the first recipient of the Chancellor's Distinguished Librarianship Award in 1990. Mason also became a member of the KU graduate faculty and served as a courtesy professor in the English Department, as well as becoming a mentor in the University Scholars program. Mason authored and co-authored 4 books, 17 articles, and over a dozen scholarly papers, as well as serving in leadership positions in the Rare Books and Manuscripts Section (RBMS) of the American Library Association.

Sandy Mason retired from KU in 1999 after 42 years of service. She passed away in 2011 and left a large estate gift from her retirment account to benefit the Spencer Research Library and establish the Ann Hyde Fellowship for Medieval and Early Modern British and European Manuscripts in honor of Ann Hyde.