Isaac Minis Hays was born on July 26, 1847, in Philadelphia, Pennsylvania.

He was a physician, ophthalmologist, editor, author, and librarian. He graduated from the University of Pennsylvania (A.B., 1866; M.D., 1868; M.A., 1869). Hays wrote or edited several works in his field of ophthalmology, including the American edition of J. Soelberg Wells’ Treatise on the Diseases of the Eye (1873) and a statistical survey entitled “Blindness: Its Frequency, Causes and Prevention” for William F. Norris and Charles A. Oliver’s System of Diseases of the Eye (1897). In 1878, he succeeded his father as editor of the American Journal of Medical Sciences and several years later, he converted a sister publication of the Journal, the monthly Medical News and Library, to a weekly format. In 1872, he was elected a Fellow of the College of Physicians of Philadelphia. In 1873, he was appointed to the Library Committee of the College and pursued its work with creativity and energy. In 1886, he was elected to membership in the American Philosophical Society (APS) and served as its librarian from 1897 until his retirement in 1922. He purchased a card catalogue and hired a professional cataloger. For a library cataloging system, Hays adopted the Dewey Decimal Classification system to replace the “philosophical” classification of former APS Librarian J. Peter Lesley (1819-1903). He sent the neglected books for binding, sold duplicate volumes, and withdrew books outside the library’s fields of interest. One of his most impressive accomplishments was a fifteen-year project to bind and catalogue the papers of Benjamin Franklin.

In 1873, he married Emma Wood (1847–1916). He died on June 5, 1925, in Philadelphia, Pennsylvania.