From left to right: Arthur Griffith, Edmund Duggan, Michael Collins, Robert Barton, (at back) Erskine Childers (sec), George Gavin Duffy and John Chartres (sec).

Éamon de Valera sent the Irish plenipotentiaries to the 1921 negotiations in London with several draft treaties and secret instructions from the cabinet. The Irish delegates set up headquarters in 22 Hans Place, Knightsbridge. The first two weeks of the negotiations were spent in formal sessions. Upon the request of Arthur Griffith and Michael Collins, the two delegations began informal negotiations, in which only two members of each negotiating team were allowed to attend. On the Irish side, these members were always Collins and Griffith, while on the British side, Neville Chamberlain always attended, though the second British negotiator would vary from day to day. In late November, the Irish delegation returned to Dublin to consult the cabinet according to their instructions.

When they returned, Collins and Griffith hammered out the final details of the treaty, which included British concessions on the wording of the oath and the defence and trade clauses, along with the addition of a Boundary Commission to the treaty and a clause upholding Irish unity. Collins and Griffith in turn convinced the other plenipotentiaries to sign the treaty. The final decisions to sign the Treaty was made in private discussions at 22 Hans Place at 11.15am on 5 December 1921. Negotiations closed by signing on at 2.20am 6 December 1921. It has been said that at the last minute Lloyd George threatened a renewal of war if the Treaty was not signed at once, but this was not mentioned as a threat in the Irish memorandum about the close of negotiations, merely a reflection of the reality.
Éamon de Valera called a cabinet meeting to discuss the treaty on 8th December, where he came out against the treaty as signed. The cabinet decided by 5 votes to 3 to recommend the Treaty to the Dáil on 14 December.