January 1 - The Central Bank of Ireland becomes the banker of the Government of Ireland in succession to the Bank of Ireland in accordance with the Central Bank Act 1971, completing its transition from a currency board to a fully operating central bank.
January 4 - John McQuaid retires after thirty years as Roman Catholic Archbishop of Dublin to be succeeded by Dermot Ryan. The ecclesiastical prohibition on Catholics entering Trinity College is relaxed.
January 22 - Taoiseach, Jack Lynch, and Minister for Foreign Affairs, Patrick Hillery, sign the Treaty of Accession to the European Communities.
January 30 - Bloody Sunday: thirteen unarmed civilians are shot dead in Derry as British soldiers open fire on a banned civil rights march.
January 31 - Taoiseach Jack Lynch announces a national day of mourning following the events in Derry the previous day.