The collection consists of Thomas McCarthy's writings, personal and literary diaries, correspondence, records from work with various arts and cultural heritage organizations, clippings and printed materials, transcriptions and recordings of interviews and events, and files related to creative writing instruction. Materials span from McCarthy's years as a student in the early 1970s through the close of the 2010s; they document his career as a poet, novelist, nonfiction writer, and editor, and to a lesser extent his work as an arts administrator, teacher, and librarian.

McCarthy's writings include handwritten and typescript drafts, proofs, galleys, and cover designs for his published works organized by book, as well as chronological poetry notebooks in which he composed early drafts and recorded notes from his research. The writings are accompanied by copious source materials, including clippings, documents, photographs, and memorabilia, which reflect his use of Irish history and politics as content and background for his work. In addition to McCarthy's poetry, fiction, and nonfiction books, there are draft materials related to film and play treatments, reviews and short essays, as well as a small number of writings by others for projects he supported. The collection also contains an extensive series of personal and literary diaries spanning five decades, which contain McCarthy's reflections on his life, as well as his commentary on contemporary politics, literature, and other topics. His correspondence also documents both professional and personal matters and includes correspondence with a number of Irish poets and writers, including Seamus Heaney, Molly Keane, Thomas Kinsella, Desmond O'Grady, Dennis O'Driscoll, Theo Dorgan, and dozens of others.

The collection also includes records McCarthy kept from his work with various arts and cultural heritage organizations, including Cork 2005, where he was the assistant director on a project to manage Cork's designation as a European Capital of Culture, and the Triskel Arts Centre in Cork, where he was the director from 1997 to 2003. There are also files on his role as a literary editor for Stet, Poetry Ireland, and Cork Review; projects related to Cork City Libraries; and his membership in Aosdána, an Irish association of artists. Other materials documenting McCarthy's professional career include recordings, transcripts, and publicity materials for interviews and events and a small number of teaching materials from creative writing workshops he taught. There is also a group of clippings, scrapbooks, printed materials, and other items that McCarthy collected documenting his own career, as well as Irish literature, history, and politics more broadly. These materials include additional research for his writings along with some personal photographs and papers.