The Treason (Ireland) Act 1821 (1 & 2 Geo. 4. c. 24) is an act of the Parliament of the United Kingdom. It extended most of the English Treason Act 1695 (7 & 8 Will. 3. c. 3) to Ireland. Previously the 1695 act only applied to England and Scotland (having been extended to Scotland by the Treason Act 1708 (7 Ann. c. 21)).
The whole act was repealed for the Republic of Ireland by the Statute Law Revision Act 1983.
As originally enacted, section 1 extended sections 2 to 5 of the Treason Act 1695 (7 & 8 Will. 3. c. 3) to Ireland. All but section 5 of the 1695 act were repealed by the Treason Act 1945. Therefore, today the effect of section 1 is only to extend section 5 of the act to Northern Ireland. Section 5 imposes a three-year time limit on bringing prosecutions for treason.
This section stated that the above time limit did not apply to attempts on the life of the king, or to misprision of such treason. (Similar provision had been made in section 6 of the act.) Section 2 also stated that trials for such treason or misprision were to be conducted according to the rules of evidence and procedure applicable in ordinary murder trials, which were different from the rules for treason trials. (This rule had been introduced in Great Britain by the Treason Act 1800.)
Section 2 of the act was repealed by the Treason Act 1945.