Tom Ryan was arrested at his home, near Thomastown, on the night of 5 February 1921. He was held initially in Kilkenny before he was transferred to Kilworth 'rest camp' near Fermoy in mid-March and, on 17 May, to Spike Island internment camp in Cork Harbour. Following a riot of the prisoners there in October, he was moved, on 18 November, to Maryborough (Portlaoise) Jail, and was released on 8 December, two days after the agreement of the Treaty. 

In all more than four thousand republican activists were interned at this time. Unusually, among this number, Ryan kept a daily record of his incarceration in a diary which, with the exception of the twenty days he spent at Maryborough, covers the entire remaining period of his imprisonment. 

The diary is one of the most complete and detailed of its kind to have survived. It affords an understanding at first-hand of the experience of one individual internee, over the course of the relatively long period he spent in prison. Because he was interacting constantly with the other internees, it can also be used to uncover intimate information, at a broader level, about this significant group of people within the independence movement. 

The remainder of the Ryan archive consists of material copied as part of his involvement in educational and literary activities while he was detained and includes an extensive collection of transcriptions of original poems and rhymes composed by the internees. The politics of the day and prison conditions are recurring topics. These verses also offer contemporary insights, which complement the diary and enhance the immediate nature of the Ryan manuscript collection. 

The archive allows a close reconstruction of Ryan's life as a War of Independence internee, and of republican internment more generally, during this pivotal period.