The Great Seal of Ireland was the seal used until 1922 by the Dublin Castle administration to authenticate important state documents in Ireland, in the same manner as the Great Seal of the Realm in England. The Great Seal of Ireland was used from at least the 1220s in the Lordship of Ireland and the ensuing Kingdom of Ireland, and remained in use when the island became part of the United Kingdom of Great Britain and Ireland (1801–1922), just as the Great Seal of Scotland remained in use after the Act of Union 1707. After 1922, the single Great Seal of Ireland was superseded by the separate Great Seal of the Irish Free State and Great Seal of Northern Ireland for the respective jurisdictions created by the partition of Ireland.

Use The office of "Lord Keeper of the Great Seal of Ireland" was held by the Lord Chancellor of Ireland. The Chancellor was presented with the physical seal upon taking his oath of office, and it was otherwise kept in the Court of Chancery. When the Chancellor was absent, Lords Commissioners of the Great Seal were appointed.O'Flanagan 1870, Vol.1 p.16 The seal was affixed to documents issued by the Privy Council of Ireland and its head the chief governor (latterly called the Lord Lieutenant). In the fifteenth century, the Chief Governor was generally non-resident and was represented by a Lord Deputy.Wood 1922, p.208 The Governor or Deputy would issue a type of writ called a fiant to the Lord Chancellor, mandating the issue of a patent ("letters patent") under the Great Seal.Wood 1922, p.217 In the fourteenth century, the Chancellor was entitled to a guard of six men-at-arms and twelve mounted archers, in part to protect the seal in his custody.Gilbert 1865, pp.209–10; O'Flanagan 1870, Vol.1 p.47 When the Lord Chancellor went as a judge of assize he would take the Great Seal with him, despite constant complaints about "the dangers of the roads".Patent Roll 11 Henry IV: "The Chancellor of Ireland has gone on assize in Munster.. with the Great Seal of Ireland... If the Lord Chancellor was unable for whatever reason to transact business, the Crown might designate another senior judge to act in his place without the Great Seal. The Chief Governor was appointed in London under the Great Seal of England, but a 1498 Act allowed a vacancy to be temporarily filled by the Dublin administration under the Irish seal.Gilbert 1865, pp.464–5 This practice was applied several times in the 1690s. In the fifteenth century, the Governor was appointed under the king's privy sealWood 1922, p.213 and appointed his Deputy under the Irish seal.Wood 1922, p.212 From 1700 to 1767, non-resident Lords Lieutenant were appointed under the British Great Seal, and would in turn use the Irish seal to appoint resident Lord Justices as deputies.

Before the Act of Union 1800, any bill passed by the Parliament of Ireland and approved by the Privy Council of Ireland was sent to London under the Great Seal of Ireland and, if approved by the Privy Council of England (later the Privy Council of Great Britain), was returned under the Great Seal of the Realm to be enacted.Gilbert 1865, pp.455–6 This procedure was required both under Poynings' Law (1495) and under the Constitution of 1782 which amended it. Parliament was summoned under the Great Seal of England rather than that of Ireland, even after 1782.21 & 22 George III c.47 [Ir] "An Act to regulate the Manner of passing Bills, and to prevent Delays in summoning of Parliament" Grierson (1794) vol. 7 pp. 154–155 A subsidiary change in 1782 was that judges of the Irish admiralty court were appointed under the Irish seal, not the English one.21 & 22 George III c.50 [Ir.] "An Act for Securing the Independency of Judges, and the Impartial Administration of Justice" Grierson (1794) vol. 7 p. 157;

Titles in the Peerage of Ireland were originally created under the English seal. After the Williamite War they were usually created under the Irish seal, but creations under the British seal continued, even after the Constitution of 1782, until the Act of Union 1800. Robert Raymond, 1st Baron Raymond wrote that, under the British seal, the Irish nature of the peerage had to be made explicit. Sometimes a single patent created separate titles in the Irish and English/British peerages for the same person. When Lord Thurlow faulted Lord Loughborough for creating Irish peers under the British seal, Lord Eldon said Thurlow had also done so. After the Union, the question of whether Irish peers appointed under the British seal were entitled to vote for Irish representative peers was considered by the Committee for Privileges of the House of Lords in 1805, and affirmed in 1806.

The 1289 "ordinance for the State of Ireland" forbade purveyance except by a commission under the Great Seal of Ireland.Gilbert 1865, p.565 From the Tudor Reconquest, appointments to the Irish judiciary were made entirely under the Irish seal.

History An Irish chancery was established in 1232 separate from the English chancery, and all documents issued from the Irish chancery were sealed with the "great seal of the king used in Ireland". Most thirteenth-century land grants continued to be issued in England with the English seal, and then sent to the Irish chancery to be enrolled. In 1256, King Henry III granted the Lordship of Ireland to his heir, the future Edward I, and ordered that Edward's personal seal should have "royal authority" there.Gilbert 1865, p.103 Henry took Ireland back from Edward in 1258. Robert de Vere, Duke of Ireland was similarly authorised to use his own great seal by Richard II in 1385;O'Flanagan 1870, Vol.1 p.49 Richard ordered de Vere's seal to be broken in 1389.Gilbert 1865, pp.259–60 In the 1300s, pardons for felony were granted under both the Irish and the English seals.

In 1417, the Chancellor, Laurence Merbury, refused to authenticate with the seal a petition to the King from the Parliament on the state of Ireland.Gilbert 1865, p.310Statute Law Revision Act 2007; 1421 (9 Hen. 5) c. 5: "Complaint as to Sir Laurence Merbury, Chancellor, having refused to affix the Great Seal to a message for the King" In 1423, the Chancellor Richard Talbot, archbishop of Dublin, refused to acknowledge Edward Dantsey, Bishop of Meath, as Deputy because the Governor, Edmund Mortimer, 5th Earl of March, had appointed Dantsey with his privy seal instead of the Great Seal. In July 1442, chancellor Richard Wogan fled Ireland after being accused of crimes, including stealing the Great Seal, which was soon handed over to Thomas Nortoun of St Saviour's Priory, Dublin by a person whom Nortoun refused to name to the Privy Council, citing the seal of confession. In 1460, Richard of York, under threat of arrest in England, fled to Ireland and persuaded the parliament to pass a declaration of independence stating in part that Ireland was "corporate of itself" and that "henceforth no person or persons being in the said land of Ireland shall be, by any command given or made under any other seal than the said seal of the said land, compelled to answer to any appeal or any other matter out of the said land".Gilbert 1865, pp.367–71 The Lord Deputy Gerald FitzGerald, 8th Earl of Kildare refused Edward IV's command to annul this, and it was not until Poynings' Parliament in 1495 that this was done.10 Hen. 7 c. 23 [Rot. Parl. cap. 40] "An Act repealing a Parliament holden at Drogheda, before Robert Prestone, lord of Gormanstowne" Grierson (1786) vol. 1 p. 57

In 1478, after Kildare was replaced as Lord Deputy by Henry Grey, 4th (7th) Baron Grey of Codnor, the Lord Chancellor Rowland FitzEustace, 1st Baron Portlester, who was Kildare's father-in-law, organised a campaign of non-co-operation with the new Deputy and refused to hand over the Great Seal, making the conduct of official business impossible. Kildare argued that Grey had been appointed under the privy signet instead of the Irish Great Seal. King Edward IV ordered Thomas Archbold, the Master of the Royal Mint in Ireland, to strike a new Great Seal, "as near as he could to the pattern and fabric of the other, with the difference of a rose in every part". The King decreed that the Seal held by Portlester was annulled, and that all acts passed under it were utterly void;Statute Law Revision Act 2007; 1478 (18 Edw. 4 sess. 3) c. 11: "All writs under the Great Seal to be void until Sir Roland Fitz Eustace restore it to the Lord Deputy; meanwhile a new seal to be made" but to no avail. So effective was the campaign of obstruction that after a few months Lord Grey was forced to return to England.Gilbert 1865, pp.403–7

In 1484, clerk James Collynge was charged with forging the Great Seal of Ireland for a fake pardon to the treasurer of Limerick Cathedral, and outlawed unless he appeared before the Chief Justice of the Common Pleas.; ; Statute Law Revision Act 2007; 1484 (1 Ric. 3) c. 23 "James Collynge to appear to answer charges of forging the Great Seal of Ireland"

One of the developments which Henry VII and the Tudor Reconquest of Ireland sought to reverse was that the Lord Deputy's private seal, kept by his secretary, was being used in place of the Great Seal of Ireland.

In 1638, Lord Chancellor Viscount Loftus refused to kneel before Lord Deputy Thomas Wentworth when delivering the Great Seal to him, contributing to the breakdown in their relationship. In 1662, the fee to the Lord Chancellor for patents under the Great Seal was increased to 10 shillings sterling per patentee.14 & 15 Chas. 2 sess. 4 c.21 [Ir] An Act for increasing the Fee of the Seal due to the Lord Chancellor in Ireland Grierson (1794) vol. 1 p. 610 The 1722 patent for Wood's halfpence was issued under the British seal rather than the Irish, which was among the complaints Jonathan Swift made in his Drapier's Letters condemning the currency.

During a lawsuit between the Marquess of Donegall and the Irish Society over fishing rights in Lough Neagh, Viscount Pery argued that the Society's 1662 charter was invalid as it was made under the English seal rather than the Irish one; the Irish Parliament passed an act in 1795 validating all land grants made under the English seal.35 Geo. 3 c. 39 [Ir.] "An Act for confirming Grants heretofore made by Patents under the Great Seal of England" Grierson (1799) vol. 10 p. 198; The Constitution of 1782 removed the role of the British great seal in Irish legislation. Napper Tandy of the Society of United Irishmen challenged his 1792 arrest on the grounds that government officials, from the Lord Lieutenant down, had been appointed under the British rather than the Irish seal. This was intended not to persuade the judges, who vehemently rejected the argument, but to increase public sympathy.

The Act of Union 1800 provided that the Great Seal of Ireland could continue to be used in Ireland, and that at elections to the Westminster parliament for constituencies in Ireland, the writs and certified returns would be under the Irish rather than the British seal.Act of Union (Ireland) 1800, Article 8, sections 8 and 10. In 1826–7, when Sir William MacMahon as Master of the Rolls in Ireland had a dispute with the Lord Chancellor of Ireland, he appealed to the Home Secretary in London rather than the Lord Lieutenant in Dublin on the ground that his appointment as Master of the Rolls was under the British seal rather than the Irish one.

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