He remained inactive from politics until after the resignation of Richard Cromwell, when he was re-appointed to a position in the army in 1659. He prevented the sitting of the Rump Parliament and created a Committee of Safety with which to run the interim government. However, George Monck's march south caused Lambert's army to disintegrate and he was imprisoned in the Tower of London in March 1660. He made one final attempt to resist the Restoration of 1660 after escaping a month later, but his support had dwindled. He spent the remaining 24 years of his life imprisoned, first on Guernsey, and then on Drake's Island where he died in the winter of 1683–84.
Lambert, born at Calton Hall, Kirkby Malham, near Skipton in the West Riding of Yorkshire, of a long-established family, studied law at the Inns of Court in London. In 1639 he married Frances Lister, daughter of Sir William Lister.
In September 1642, Lambert was appointed a captain of horse in the Parliamentary army of the English Civil War, commanded by Ferdinando, Lord Fairfax. Within a year, he was colonel of a cavalry regiment, and distinguished himself at the siege of Hull in October 1643. Early in 1644 he did good service at the battles of Nantwich and Bradford. At Marston Moor (2 July 1644) Lambert's own regiment was routed by the charge of Goring's horse; but he cut his way through with a few troops and joined Oliver Cromwell on the other side of the field.
When the New Model Army formed in the beginning of 1645, Colonel Lambert was appointed to succeed Sir Thomas Fairfax in command of the northern forces, with the title of commissary-general. Fairfax was soon replaced by Sydnam Poyntz, and under this officer Lambert served in the Yorkshire campaign of 1645, receiving a wound before Pontefract. In 1646 he was given a regiment in the New Model, serving with Sir Thomas in the west of England, and he was a commissioner, with Cromwell and others, for the surrender of Oxford in the same year. "It is evident that he was from the first regarded as an officer of exceptional capacity and specially selected for semi-political employments".
When the quarrel between the Army and Parliament began, Lambert supported the Army's cause. He assisted Henry Ireton in drawing up the addresses and remonstrances issued by the Army, both men having had some experience in law. Early in August 1647 Lambert was sent by Fairfax as Major-General to take charge of the forces in the northern counties. His management of affairs in those parts is praised by Whitelocke. He suppressed a mutiny among his troops, kept strict discipline and hunted down the moss-troopers who infested the moorland country.
At the start of the Second English Civil War Lambert now a young general of twenty-nine, was more than equal to the situation. He had already left the sieges of Pontefract Castle and Scarborough Castle to Colonel Edward Rossiter, and hurried into Cumberland to deal with the English Royalists under Sir Marmaduke Langdale. With his cavalry he got into touch with the enemy about Carlisle and slowly fell back, fighting small rearguard actions to annoy the enemy and gain time, to Bowes and Barnard Castle. Langdale did not follow him into the mountains, but occupied himself in gathering recruits and supplies of material and food for the Scots. Lambert, reinforced from the Midlands, reappeared early in June and drove him back to Carlisle with his work half finished. About the same time the local horse of Durham and Northumberland were put into the field by Sir Arthur Hesilrige, governor of Newcastle, and under the command of Colonel Robert Lilburne won a considerable success (30 June) at the River Coquet.
This reverse, coupled with the existence of Langdale's force on the Cumberland side, practically compelled Hamilton to choose the west coast route for his advance, and his army began slowly to move down the long couloir between the mountains and the sea. The campaign which followed is one of the most brilliant in English history. When the Scottish army under James Hamilton, 1st Duke of Hamilton invaded England in the summer of 1648, Lambert was obliged to retreat; but Lambert continued to harass the invaders till Cromwell came up from Wales and the Scottish army was destroyed in the three days' fighting at the Battle of Preston fought largely at Walton-le-Dale near Preston in Lancashire. After the battle Lambert's cavalry headed the chase, pursuing the defeated army, and finally surrounded it at Uttoxeter, where Hamilton surrendered to Lambert on 25 August 1648. Lambert then led the advance of Cromwell's army into Scotland, where he was left in charge on Cromwell's return. From December 1648 to March 1649 he was engaged in the successful siege of Pontefract Castle; Lambert was thus absent from London at the time of Pride's Purge and the trial and execution of King Charles I.
When Cromwell was appointed to the command of the war in Scotland (July 1650), Lambert went with him as major-general and second in command. He was wounded at Musselburgh, but returned to the front in time to take a conspicuous share in the victory of Dunbar. He himself repulsed a surprise attack by the Covenanters at the Battle of Hamilton on 1 December 1650. In July 1651 he was sent into Fife to get in the rear and flank of the Scottish army near Falkirk, and force them to decisive action by cutting off their supplies. This mission, in the course of which Lambert won an important victory at Inverkeithing, was so successful that Charles II, as Lambert had foreseen, made for England. Lambert's part in the general plan of the resulting Worcester campaign was carried out brilliantly (including his capture of Upton-Upon-Severn), and in the crowning victory of Worcester he commanded the right wing of the English army, and had his horse shot under him. Parliament granted him lands in Scotland worth £1000 per annum.
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). He made extensive preparations; parliament, however, reconstituted the Irish administration and Lambert refused to accept office on the new terms. He then began to oppose the Rump Parliament. 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.
At the same time Lambert was consulted by the parliamentary leaders as to the possibility of dismissing Cromwell from his command, and on 15 March 1653 Cromwell refused to see him, speaking of him contemptuously as "bottomless Lambert". On 20 April 1653, however, Lambert accompanied Cromwell when he dismissed the Council of State, on the same day as the forcible expulsion of the parliament.
Lambert now favoured the formation of a small executive council, to be followed by an elective parliament whose powers should be limited by a written instrument of government. 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. He was invited, with Cromwell, Harrison and John Desborough, to sit in the nominated "Barebones Parliament" of 1653; and when the unpopularity of that assembly increased, Cromwell drew nearer to Lambert. 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. On 12 December 1653, the parliament resigned its powers into Cromwell's hands, and on 13 December Lambert obtained the consent of the officers to the Instrument of Government, in the framing of which he had taken a lead. He was one of the seven officers nominated to seats in the council created by the Instrument.
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.
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. In the parliament of this year, and again in 1656, Lord Lambert, as he was now styled, sat as member for the West Riding. He was one of the major-generals appointed in August 1655 to command the militia in the ten districts into which it was proposed to divide England, and who were to be responsible for the maintenance of order and the administration of the law in their several districts.
Lambert took a prominent part in the Committee of Council which drew up instructions to the administrative major-generals. He was the organiser of the system of police which these officers were to control. Samuel Gardiner conjectures that it was through divergence of opinion between the protector and Lambert in connection with these "instructions" that the estrangement between the two men began. 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.
A hundred officers headed by Charles Fleetwood and Lambert waited on the protector, and begged him to put a stop to the proceedings. Lambert was not convinced by Cromwell's arguments, and their complete estrangement, personal as well as political, followed. On his refusal to take the oath of allegiance to the protector, Lambert was deprived of his commissions, receiving instead a pension of £2000 a year. He retired from public life to Wimbledon; but shortly before his own death Cromwell sought a reconciliation, and Lambert and his wife visited Cromwell at Whitehall.
When Richard Cromwell was proclaimed protector (3 September 1658), his chief difficulty lay with the army, over which he exercised no effective control. Lambert, though holding no military commission, was the most popular of the old Cromwellian generals with the rank and file of the army, and it was very generally believed that he would install himself in Oliver Cromwell's seat of power. 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. Lambert at first gave a lukewarm support to Richard Cromwell, and took no part in the intrigues of the officers at Fleetwood's residence, Wallingford House. He was a member of the Third Protectorate Parliament which met in January 1659, and when it was dissolved in April under compulsion of Fleetwood and Desborough, he was restored to his commands. 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.
When the parliament, in an attempt to control the power of the army, withheld from Fleetwood the right of nominating officers, Lambert was named one of a council of seven charged with this duty. 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. He promoted a petition from his army that Fleetwood might be made lord-general and himself major-general. The republican party in the House took offence. The Commons (12 October 1659) cashiered Lambert and other officers, and retained Fleetwood as chief of a military council under the authority of the speaker. On the next day Lambert caused the doors of the House to be shut and the members kept out. On 26 October a new Committee of Safety was appointed, of which he was a member. He was also appointed major-general of all the forces in England and Scotland, Fleetwood being general.
Lambert was now sent with a large force to meet George Monck, who was in command of the English forces in Scotland, and either negotiate with him or force him to terms. Monck, however, marched southward. Lambert's army began to melt away, and he was kept in suspense by Monck till his whole army deserted and he returned to London almost alone. Monck marched to London unopposed. The excluded Presbyterian members were recalled. Lambert was sent to the Tower (3 March 1660), from which he escaped a month later. He descended a silk rope and aided by six men was taken away by barge. He tried to rekindle the civil war in favour of the Commonwealth by issuing a proclamation calling on all supporters of the "Good Old Cause" to rally on the battlefield of Edgehill. But he was recaptured on 22 April at Daventry by Colonel Richard Ingoldsby, a regicide who hoped to win a pardon by handing Lambert over to the new regime. He was kept imprisoned in the Tower of London and then transferred to Castle Cornet on the island Guernsey.
On the Restoration Lambert was exempted from prosecution by an address of both Houses of the Convention Parliament to the king, but the Cavalier Parliament in 1662 charged him with high treason. In April 1662 General Lambert was, with Sir Henry Vane, brought to England and tried in June 1662. On 25 July a warrant was issued to Lord Hatton, the governor of Guernsey, to take into his custody "the person of John Lambert, commonly called Colonel Lambert, and keep him a close prisoner as a condemned traitor until further orders". 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".
In 1662 Lambert was imprisoned in Guernsey. In 1667 he was transferred to Drake's Island in Plymouth Sound, at the entrance to the Hamoaze, and he died there during the severe winter of 1683–84. The site of his grave is now lost but he was laid to rest at St Andrews Church in Plymouth on 28 March 1684.
He was the author of the Instrument of Government, the first written constitution in the world codifying sovereign powers. The Instrument of Government was replaced in May 1657 by England's second, last, and extinct codified constitution, the Humble Petition and Advice.
It has been said that Lambert's nature had more in common with the royalist than with the puritan spirit. Vain and ambitious, he believed that Cromwell could not stand without him; and when Cromwell was dead, he imagined himself entitled to succeed him. As a soldier he was far more than a fighting general and possessed many of the qualities of a great general. He was an able writer and speaker, and an accomplished negotiator and took pleasure in quiet and domestic pursuits. He learnt his love of gardening from Lord Fairfax, who was also his master in the art of war. He painted flowers, besides cultivating them, and was accused by Mrs Hutchinson of "dressing his flowers in his garden and working at the needle with his wife and his maids".