In the 1850s and 1860s he assisted with the re-cataloging of the Harvard College library, producing America's first public card catalog.

The card system proved more flexible for librarians and far more useful to patrons than the old method of entering titles in chronological order in large books.

During that time, Cutter began designing a distinct cataloging schema for the library's outdated system.

[2] During the 1857–1858 school year, Cutter rearranged the library collection on the shelves into broad subject categories along with classmate Charles Noyes Forbes.

Cutter introduced characteristic structures and philosophies such as inter-library loan and furnishing every book with a pouch in the rear to encase a card in order to keep track of the item's circulating status.

He spent a lot of time discussing practicalities, such as how the library arranged adequate lighting and controlled moisture in the air to preserve the books.

[8] When Cutter began to delegate a new system for the library he initially chose the Dewey Decimal Classification, however he determined it was more beneficial to assign a more distinct adaptation for the collection.

[9] Cutter was commissioned on at least one occasion to propose an architectural conception for the University of Toronto Library which had recently been consumed by a massive conflagration.

[10] In response to the library's requests, Cutter admonished, "It is of little use to have a fire proof stack if the rest of the building gets afire".

Judge Charles E. Forbes left a considerable amount of money to the town to start a library.

Thus small libraries who did not like having to deal with unnecessarily long classification numbers could use lower levels and still be specific enough for their purpose.

Today, Charles Ammi Cutter might be surprised to see his own portrait hanging over the reference librarians' desk in the Forbes Library in Northampton.