Charles W. Mann, Jr. was born December 29, 1929 in Altoona, Pennsylvania, to Charles W. Mann, a railroad worker, and Elizabeth (Warner) Mann. Mann's 10-year marriage to Nan Gullo produced a daughter, Molly. The couple divorced in 1970 and Mann later married Nancy McCall, a medical archivist.

Mann graduated from The Pennsylvania State University with a bachelor's degree in history and social studies in 1952, and received a master's degree in English in 1954. While a student at Penn State, Mann worked at the Pattee Library shelving books for 50 cents an hour. He began working as a library assistant in 1954, and became the first head of the Rare Books Room in 1958. He was then sent to Rutgers University to acquire a library degree specializing in rare books librarianship, which he received in 1961. Named librarian in 1972, he also became chief of rare books and special collections. Mann was made a full professor at Penn State in 1975, teaching English and comparative literature. Additionally, Mann lectured widely, wrote hundreds of book reviews, and was involved with the editing of several publications. In 1994, he became the first Dorothy Foehr Huck Chair for Special Collections in the University Libraries.

Teaming up with Penn State Hemingway scholar, Philip Young, Mann helped write The Hemingway Manuscripts, published in 1969. The first detailed inventory of Hemingway's unpublished work, the book included dozens of unpublished writings discovered by Mann. Among the previously unknown material were a novel, Jimmy Breen; a short story, Summer People; and a ten-page letter from F. Scott Fitzgerald critiquing The Sun Also Rises. Additionally, Mann found the ninth known copy of Christopher Marlowe's Tamburlaine. Mann had an in-depth knowledge of the history of books and bookmaking, bibliography, architecture, the history of photography, and the literature of the former British Commonwealth. He has been credited with building Penn State's rare books and manuscripts collections from nothing. An expert on the publishing history of John O'Hara, Mann helped bring O'Hara's manuscript collection to Penn State. He also contributed to Fitzgerald/Hemingway Annual, American Reference Books Annual, Library Journal, History of Photography, and Literature East and West.

Mann received many awards during his career recognizing his work and contributions to literature and learning. He was the recipient of a resolution of commendation from the College of Liberal Arts in 1963, and was named a Friend of the Hawthorne Project in 1964. In 1974 he was the winner of the first award for Outstanding Contributions to the Pennsylvania State University Libraries. Mann received the McKay Donkin Award for Special Service to Faculty and Staff in 1981. He was also an Honorary Fellow of the Institute for the Arts and Humanistic Studies, as well as an Honorary Fellow of the Australian-New Zealand Studies Center for contributions to Australian-American relations. A member of the Grolier Club, Mann prepared an exhibit for the organization focusing on London's Great Exhibition of 1851 and the history of the Crystal Palace, which ran from December of 1976 to January of 1977. Mann was a member of many professional societies including Bibliographic Society of America, Milton Society of America, International Joseph Conrad Society, American Library Association (Rare Books Section), International Ernest Hemingway Society, Pennsylvania Historical Association, and American Manuscript Society.

Mann died of a heart attack on July 17, 1998, at his home in Baltimore at the age of 68.