At the age of fifteen Barrett joined the Irish Volunteers, a revolutionary organisation that hoped to established independence for Ireland. He remained active during the War of Independence. He took the republican side in the subsequent Civil War that followed the signing of the Anglo-Irish Treaty. Barrett was arrested in September 1922 and suffered much hardship during his imprisonment. While in prisoned he embarked on a 22-day hunger strike which undoubtedly affected his health in later life. Upon his release Barrett and his siblings set about rebuilding their business. It proved difficult at a time when political tensions divided friends and neighbours and boycotts of certain shops and businesses were regular occurrences.