As a minor, John Lambert became the ward of Sir William Lister, a long-standing family friend, who appears to have paid for his education at Trinity College, Cambridge.

Although Lambert and the Listers followed Lord Fairfax in supporting Parliament, they were related by marriage and blood to Royalists like Sir Henry Slingsby and John Belasyse.

[5] In January 1645, Thomas Fairfax was appointed commander of the New Model Army and Lambert promoted Commissary General of the Northern Association, effectively acting as his deputy.

[6] During the siege of Pontefract Castle, one of the few Royalist positions left in the north, he was wounded and defeated on 1 March by a relief force led by Marmaduke Langdale.

[8] Lambert transferred to the New Model, although shortage of troops meant he remained in the north until just after Naseby in June 1645, when he served in Fairfax's western campaign.

He supervised the capture of Dartmouth in January 1646 and was present at the sieges of Truro in March, Exeter in April and finally Oxford in June, which ended the First Civil War.

[9] Victory exposed long-standing divisions between mostly Presbyterian moderates led by Denzil Holles who dominated Parliament, and radicals within the New Model Army, focused around Cromwell.

Originating in differences over the political settlement with Charles I, it was exacerbated by financial issues and by March 1647, the New Model Army was owed more than £3 million in unpaid wages.

Parliament ordered it to Ireland, stating only those who agreed would be paid; when their representatives demanded full payment for all in advance, it was disbanded, but the army refused to comply.

Working with Ireton, Lambert helped draw up the army's terms for a peace settlement with the king, although the extent of his involvement has been challenged by some historians.

Fearing Charles was going to be restored without significant concessions, the Army Council took control of the city on 7 August and in October expelled their leading opponents from Parliament, the so-called Eleven Members.

[14] Most of the New Model Army was with Fairfax, who was suppressing revolts in Essex and Kent, and Cromwell in South Wales, leaving Lambert facing a precarious situation in the north.

[16] In October 1651 Lambert was made a commissioner under the Tender of Union to settle the affairs of Scotland, and on the death of Ireton he was appointed lord deputy of Ireland (January 1652).

In the Council of Officers he headed the party desiring representative government, as opposed to Harrison who favoured an oligarchy of "God-fearing" men, but both hated the Rump of the Long Parliament, and joined in urging Cromwell to dissolve it by force.

As the ruling spirit in the Council of State, and the idol of the army, he was seen as a possible rival of Cromwell for the chief executive power, while the royalists for a short time had hopes of his support.

In November 1653 Lambert presided over a meeting of officers, when the question of constitutional settlement was discussed, and a proposal made for the forcible expulsion of the nominated parliament.

[16] In the foreign policy of the Protectorate Lambert called for alliance with Spain and war with France in 1653, and he firmly withstood Cromwell's design for an expedition to the West Indies.

[16] In the debates in parliament on the Instrument of Government in 1654 Lambert proposed that the office of Lord Protector should be made hereditary, but was defeated by a majority which included members of Cromwell's family.

At all events, although Lambert had himself at an earlier date requested Cromwell to take the royal dignity, when the proposal to declare Oliver king was started in parliament (February 1657) he at once opposed it.

Richard Cromwell's adherents tried to conciliate him, and the royalist leaders made overtures to him, even proposing that Charles II should marry Lambert's daughter.

He headed the deputation to Lenthall in May 1659 inviting the return of the Rump Parliament, which led to the tame retirement of Richard Cromwell; and he was appointed a member of the Committee of Safety and of the Council of State.

The parliament's evident distrust of the soldiers caused much discontent in the army; while the absence of authority encouraged the royalists to make overt attempts to restore Charles II, the most serious of which, under Sir George Booth and the earl of Derby, was crushed by Lambert near Chester on 19 August 1659.

On 18 November following, directions were given from the king to Lord Hatton to "give such liberty and indulgence to Colonel John Lambert within the precincts of the island as will consist with the security of his person".