Upon graduation, Mumford was granted a tuition scholarship to attend Trinity College in Durham, North Carolina; his educational goal focused on preparing for a teaching career.

Outside of the society, Mumford participated in the Physics Club, Phi Beta Kappa, and acted in two dramatic productions on top of working in the library as a student assistant.

College Librarian Joseph Penn Breedlove offered Mumford a full-time position and he accepted so that he could continue to work towards a master's degree that would help with his dreams of a teaching career.

His time spent at the CPL can be marked by improved growth (financially and physically) and increased public awareness and support.

His efforts with various ALA committees and his work with the Film Council of America and the Great Books Foundation led to his nomination and selection as President of the American Library Association in 1954.

We should not lose sight of the fact that maintaining man's right to knowledge and freedom to choose his reading is an empty achievement if we do not make available to him the material from which he can select and choose ... Freedom to read is an academic right, important as a principle, but meaningless in effect unless library resources are made available to those who lack them.Mumford spent a year as ALA President and during this time helped to streamline management of the association and oversaw the establishment of the Laura Ingalls Wilder Award for substantial and lasting contributions to literature for children.

As Librarian of Congress, Mumford was able to use his oratorical skills to repair vital relationships, rebuild Congressional confidence in the library and gain much needed appropriations to improve functions and programming.

Other achievements include a ninefold total increase in appropriations, the establishment of the National Program for Acquisitions and Cataloging (NPAC), completion and distribution of the Machine-Readable Cataloging (MARC) system, an increase in services for handicapped readers, expansion of legislative research into the more dedicated Congressional Research Service, final publication of the Pre-1956 National Union Catalog, completion of the Presidential Papers Program, development of preservation programs and the establishment of the Preservation Research Laboratory, the expansion of motion picture programs, the addition of an African section and a Children's Book section, development of National Referral Center for Science and Technology, the establishment of the American Revolution Bicentennial Office and the development of the Affirmative Action Plan that provided for equality, training and scholarship of Library of Congress staff.