The Army Council was a term first used in 1647 to describe an institution which coordinated the views of all levels of the New Model Army. During the Interregnum it metamorphosed into the (Army) Council of Officers.
Having won the First English Civil War, the soldiers of the New Model Army (Army) became very discontented with the Long Parliament, for several reasons. Firstly, they had not been paid regularly and on the end of hostilities, the conservative MPs in Parliament wanted to either disband the Army or send them to fight in Ireland without receiving their back pay. Secondly, since most Parliamentarians wanted to restore the King without major democratic reforms or religious freedom, many soldiers asked why they had risked their lives in the first place — a sentiment that was strongly expressed by their elected representatives.
Two representatives, called Agitators, were elected from each regiment. The Agitators with two Army Officers from each regiment and the Generals formed a new body called the Army Council which after a rendezvous (meeting) near Newmarket on Friday 4 June 1647 issued "A Solemne Engagement of the Army, under the Command of his Excellency Sir Thomas Fairfax" to Parliament on 8 June making their concerns known and also the constitution of the Army Council so that Parliament would understand that the discontent was Army wide and had the support of officers and other ranks. This Engagement was read out to the Army at a general Army rendezvous on 5 June.
Having come under the influence of London radicals called the Levellers, the troops of the Army proposed a revolutionary new constitution named the Agreement of the People, which called for almost universal male suffrage, reform of electoral boundaries, power to rest with the Parliament which was to be elected every two years (not the King), religious freedom and an end to imprisonment for debt.
Increasingly concerned at the failure to pay their wages and by political maneuverings by King Charles I of England and by some in Parliament, the army marched slowly towards London over the next few months. In late October and early November at the Putney Debates the Army debated two different proposals. The first the Agreement of the People and the other "The Heads of the Proposals", put forward by Henry Ireton, (son-in-law of Oliver Cromwell) for the Army Council. It was a constitutional manifesto which included the preservation of property rights and maintaining the privileges of the gentry. At the Putney Debates it was agreed to hold three further rendezvous.