In about 1861 he joined the Irish Republican Brotherhood (IRB), and soon afterwards became its treasurer. He broke with the IRB in 1881, forming a new group which assumed the title of the Invincibles, and established their headquarters in Dublin. Carey took an oath as one of the leaders. The object of the Invincibles was to remove all "tyrants" from the country, and several attempts, but without success, were made to assassinate Earl Cowper and W. E. Forster.
