The Boundary Commission was established under the Anglo-Irish Treaty that ended the Anglo-Irish War in 1921. Its purpose was to decide on the precise delineation of the border between the Irish Free State and Northern Ireland if Northern Ireland chose to secede from the Irish Free State as was widely anticipated. The Irish Free State was itself established on 6 December 1922 and encompassed all of Ireland including Northern Ireland. However on 8 December 1922, just two days later, Northern Ireland seceded from the Irish Free State by exercising its right to do so under the Treaty.

With the secession of Northern Ireland from the Irish Free State back to the United Kingdom, in accordance with the Treaty it fell to the Governments of the United Kingdom, the Irish Free State and Northern Ireland to nominate members to a Boundary Commission to delineate the precise border between the Irish Free State and Northern Ireland. While nationalists hoped for a considerable transfer of land from Northern Ireland to the Free State (reflecting the wishes of people who lived along the new border), the Northern Ireland government refused to appoint their commissioner, resulting in the British government assigning a Belfast newspaper editor to represent Northern Irish interests.

When the Commission decided initially on a very small net transfer of land to Northern Ireland (the reverse of what was expected), it was leaked to the Morning Post in 1925, causing protests from both the unionists and nationalists. In order to avoid the possibility of further disputes, the British, Irish, and Northern Ireland governments agreed to suppress the overall report, and the existing (Government of Ireland Act 1920) border was ratified by W. T. Cosgrave, Sir James Craig, and Stanley Baldwin on 3 December 1925 as part of a wider agreement including a resolution of outstanding financial matters.

The provisional border 1920 - 1925:

The Government of Ireland Act 1920 was enacted during the height of the Anglo-Irish War and partitioned the island into two separate Home Rule territories of the United Kingdom, to be called Northern Ireland and Southern Ireland. In its determination of this border, the Parliament of the United Kingdom heard the arguments of the Irish Unionist Party - but not those of most of the elected representatives of the nationalist population. Sinn Féin refused to recognise any legitimate role of that Parliament in Irish affairs and declined to attend it, leaving only the minuscule Irish Parliamentary Party present at the debates. James Craig's brother told the British House of Commons unambiguously that the six north-eastern counties were the largest possible area that unionists could "hold".

Article 12 of the Treaty:

After a clause providing for Northern Ireland (as defined by the Government of Ireland Act 1920) to opt out of the new Free State, the remainder of Article 12 declares:

Provided that if such an address (exercising Northern Ireland's right to opt out of the Irish Free State) is so presented, a Commission consisting of three persons, one to be appointed by the Government of the Irish Free State, one to be appointed by the Government of Northern Ireland, and one who shall be Chairman to be appointed by the British Government shall determine in accordance with the wishes of the inhabitants, so far as may be compatible with economic and geographic conditions the boundaries between Northern Ireland and the rest of Ireland, and for the purposes of the Government of Ireland Act, 1920, and of this instrument, the boundary of Northern Ireland shall be such as may be determined by such Commission.

Accordingly in 1922 the new Free State established the North-Eastern Boundary Bureau which had prepared 56 boxes of files to argue its case by 1925.

Within months the three governments signed the "Craig-Collins Agreement" in March 1922, in an attempt to end the conflict in Northern Ireland. Despite Article 12, the agreement envisaged a two-party conference between the Northern Irish government and the Provisional Government of Southern Ireland to establish: "(7) a. Whether means can be devised to secure the unity of Ireland" and "b. Failing this, whether agreement can be arrived at on the boundary question otherwise than by recourse to the Boundary Commission outlined in Article 12 of the Treaty", but the agreement quickly broke down for other reasons.

The Commission:

Due to the delay caused by the Irish Civil War, the Commission was appointed in 1924. The Northern Ireland government, which adopted a policy of refusing to cooperate with the Commission since it did not wish to lose any territory, refused to appoint a representative. Ultimately the Labour government in Britain and the Irish Free State government legislated to allow the UK Government to impose a representative on their behalf in order to enable the procedure to go ahead. The Commission was convened in 1925 consisting of:

Justice Richard Feetham of South Africa as Chairman (appointed by, and representing, the British Government)
Eoin MacNeill, Minister for Education (appointed by, and representing, the Free State Government)
J.R. Fisher, a Unionist newspaper editor (appointed by the British government to represent the Northern Ireland government)

The nationalist interpretation of Article 12 was that the Commission should redraw the border according to local nationalist or unionist majorities at the finely granular District Electoral Division (DED) level. Since the 1920 local elections in Ireland had resulted in outright nationalist majorities in County Fermanagh, County Tyrone, the City of Derry and in many District Electoral Divisions of County Armagh and County Derry (all north and east of the "interim" border), this might well have left Northern Ireland unviable. Unionists were content to leave the border unchanged.

The Commission's report has never been officially released, continuing to be withheld by both Governments. However the negotiating positions have been known since 1925 from the Dáil debates and newspaper reports, but are seldom mentioned in mainstream history books. The republican view was that the entire partition and Boundary Commission process was a British imperial plan to divide and control Ireland, with the demographic report suppressed; the Northern Irish unionist view was that it had all been publicised and approved by the three parliaments involved.

Premature publication:

On 7 November 1925 an English Conservative newspaper, the Morning Post, published leaked notes of the negotiations, including a draft map that suggested that parts of east Donegal would be transferred to Northern Ireland. This was seen as an embarrassment in Dublin, being contrary to the overarching purpose of the Commission, which was to award the more Nationalist parts of Northern Ireland to the Free State, and Professor MacNeill resigned on 20 November. Despite resigning, he then voted in favour of the settlement on 10 December. It is likely that the press leak caused the boundary negotiations to be swept into the wider agreement signed on 3 December.

Inter-governmental agreement Nov-Dec 1925:

McNeill's resignation suspended the Commission's work. In late November members of the Irish government visited London and Chequers to go over the ground since the Treaty and to consider the exact meaning of Article 12.
The Irish view was that it was only intended to award areas within the six counties of Northern Ireland to the Free State.
The British view was that the entire 1920 boundary was adjustable in either direction, as the Irish side had insisted in the 1921 Treaty that Northern Ireland was deemed part of Ireland until it voted to secede in December 1922, but that the net balance of property and people transferred either way would benefit the Free State.

Cosgrave emphasised that his government might fall but arrived at the idea of a larger solution including interstate financial matters after receiving a memo from Joe Brennan, a senior civil servant. On 2 December Cosgrave summed up his attitude on the debacle to the British Cabinet.

In the background, under the terms of Article 5 of the 1921 Anglo-Irish Treaty the Irish Free State had agreed to pay its share of the Imperial debt: "(5) The Irish Free State shall assume liability for the service of the Public Debt of the United Kingdom as existing at the date hereof and towards the payment of war pensions as existing at that date in such proportion as may be fair and equitable, having regard to any just claims on the part of Ireland by way of set-off or counter-claim, the amount of such sums being determined in default of agreement by the arbitration of one or more independent persons being citizens of the British Empire."

This had not been paid by 1925, in part due to the heavy costs incurred in and after the Irish Civil War of 1922-23. The main essence of the inter-governmental agreement was that the 1920 boundary would stay as it was, and, in return, Britain would not demand payment of the amount agreed under the Treaty. Since 1925 this payment was never made, nor demanded.

Diarmaid Ferriter suggests a more complex trade-off; the debt obligation was removed from the Free State and non-publication of the report, in return for the Free State dropping its claim to rule some Catholic / nationalist areas of Northern Ireland. Each side could blame the other side for the outcome. William Cosgrave admitted that the security of the Catholic minority depended on the goodwill of their neighbours.

The final agreement between the Irish Free State, Northern Ireland, and Britain was signed on 3 December 1925. Later that day the agreement was read out by Stanley Baldwin in the House of Commons. The agreement was enacted by the "Ireland (Confirmation of Agreement) Act" that was passed unanimously by the British parliament on 8-9 December. Effectively the agreement was concluded by the three governments, and the Commission then rubber-stamped it, so the publication, or not, of the Commission's report became an irrelevance. The Agreement was then formally registered with the League of Nations on 8 February 1926.

Dáil debates on the Commission, 7-10 December 1925:

In the Dáil debates on the outcome on 7 December 1925, Cosgrave mentioned that the sum due under the Imperial debt had not yet been fixed, but was estimated at £5m. to £19m. annually, Britain having a debt of over £7 billions. The Free State's annual budget was then about £25m. Cosgrave's aim was to eliminate this amount: "I had only one figure in my mind and that was a huge nought. That was the figure I strove to get, and I got it." Cosgrave also hoped that the large nationalist minority in Northern Ireland would be a bridge between Belfast and Dublin.

On the final day of debate, Cosgrave revealed that one of the reasons for independence, the elimination of poverty caused by London's over-taxation of Ireland, had not been solved even after four years of freedom:

"In our negotiations we went on one issue alone, and that was our ability to pay. Not a single penny of a counter-claim did we put up. We cited the condition of affairs in this country-250,000 occupiers of uneconomic holdings, the holdings of such a valuation as did not permit of a decent livelihood for the owners; 212,000 labourers, with a maximum rate of wages of 26s. a week: with our railways in a bad condition, with our Old Age Pensions on an average, I suppose, of 1s. 6d. a week less than is paid in England or in Northern Ireland, with our inability to fund the Unemployment Fund, with a tax on beer of 20s. a barrel more than they, with a heavier postage rate. That was our case."

His main opponent was Professor Magennis from Ulster, who particularly objected that the Council of Ireland (a mechanism for future unity by the 1970s, provided under the Government of Ireland Act 1920) was not mentioned.
There was in that wretched and much resisted Act of 1920 a provision for bringing about ultimate union. Some of our leaders would have said in those days that was all hocus-pocus, but, at all events, the Bill declared, just as the President's statement declared, that what was intended was to bring about a union of hearts. If I had the Bill by me I am confident I could read out a clause in which the seers, the diviners, and the soothsayers, who framed the Act of 1920, told us that, ultimately, it would bring about union. There was a date on which the Council of Ireland was to go out of operation, and that was a date on which by a similar joint resolution of both Parliaments-the Parliament of Ireland was to be set up. That was one of the clauses in the Act of 1920. Do we find anything to that effect in this agreement? Is there any stipulation in the four corners of this document for the ultimate setting up of a Parliament of all Ireland or anything that would appear to be a Parliament of all Ireland? No!

The government side felt that a boundary of some sort, and partition, had been on the cards for years. If the boundary was moved towards Belfast it would be harder to eliminate in the long term. Kevin O'Higgins pondered:

...whether the Boundary Commission at any time was a wonderful piece of constructive statesmanship, the shoving up of a line, four, five or ten miles, leaving the Nationalists north of that line in a smaller minority than is at present the case, leaving the pull towards union, the pull towards the south, smaller and weaker than is at present the case.

On 9 December a deputation of Ulster nationalists arrived to make their views known to the Dáil, but were turned away.

After 4 days of heated debate on the "Treaty (Confirmation of amending agreement) Bill, 1925", the boundary agreement was approved on 10 December by a Dáil vote of 71 to 20. On 16 December the Irish Senate approved by 35 votes to 7.
Non-publication of the Report:

Both Irish prime ministers agreed in the negotiations on 3 December to bury the report as part of a wider inter-governmental settlement. The remaining Commissioners discussed the matter with the politicians at length, and expected publication within weeks. However, WT Cosgrave said that he: "..believed that it would be in the interests of Irish peace that the Report should be burned or buried, because another set of circumstances had arrived, and a bigger settlement had been reached beyond any that the Award of the Commission could achieve."

Sir James Craig added that: "If the settlement succeeded it would be a great disservice to Ireland, North and South, to have a map produced showing what would have been the position of the persons on the Border had the Award been made. If the settlement came off and nothing was published, no-one would know what would have been his fate. He himself had not seen the map of the proposed new Boundary. When he returned home he would be questioned on the subject and he preferred to be able to say that he did not know the terms of the proposed Award. He was certain that it would be better that no-one should ever know accurately what their position would have been." For differing reasons the British government and the remaining two Commissioners agreed with these views. Even this inter-governmental discussion about suppressing the report remained a secret for decades.