Gentles has argued that ‘the agitators may have forced the pace of events until 4 June, but on the 5th the grandees, perhaps led by Ireton, moved for the creation of a council of the army’. Many might have had sympathy with the adjutators' agenda but wanted leadership from the officers. Later, in May 1649, a keen observer of army politics commented:

As the politicalisation of the army, in reaction to Holles' Parliamentary faction, became more pronounced, the rendezvous at Newmarket on 4–5 June 1647 saw the organisation of a more formal political structure, the General Council of the Army. Through this body the officers, in particular Ireton, sought to lead the army, officers, adjutators and men, to settlement. The army's position, written by Ireton, emerged as the Solemn Engagement of 5 June 1647.

Like most of the significant documents which emerged from the army in the period before Charles' execution, the Solemn Engagement was principally the work of Ireton, in consultation with others. The imagery employed by Walker in his portrait hints at Ireton's role as ‘penman general’ of the army. Whitelocke, present with the army at Oxford, wrote about a ‘select council’ of army – Fairfax, Ireton, Cromwell, Lambert and Fleetwood.