Childers was secretary-general of the Irish delegation that negotiated the Anglo-Irish Treaty with the British Government. He stayed at the delegation headquarters in Hans Place throughout the period of the negotiations, 11 October – 6 December 1921. However, Childers became vehemently opposed to the final draft of the agreement, particularly the clauses that required Irish leaders to take the Oath of Allegiance to the British monarch. The Treaty was approved by an exhausted Dáil voting 64–57 in January 1922. In the course of the debates some felt that Childers had been insulted by Arthur Griffith, and the matter was debated in June. The treaty continued to divide Sinn Féin and the IRA, and Ireland descended into civil war on 28 June 1922.