In December 1647 Wildman wrote a pamphlet, Putney Projects, that attacked Oliver Cromwell and Henry Ireton for betraying the New Model Army's Declaration of 14 June 1647 in the Heads of Proposals.

[3] The soldiers, explained Wildman, "desired me to be their mouth", and he argued on their behalf that the engagements entered into with the King should be cancelled, monarchy and the House of Lords abolished, and manhood suffrage established.

[3] On 18 January 1648 George Masterson, minister of Shoreditch informed against Wildman and Lieutenant-Colonel John Lilburne for promoting a seditious petition.

[11] On the release of the two prisoners the Levellers held a meeting at the Nag's Head tavern,[clarification needed] in which, says Lilburne, "the just ends of the war were as exactly laid open by Mr. John Wildman as ever I heard in my life",[12] and the party agreed to oppose the execution or deposition of the king until the fundamental principles of the future constitution were settled.

[12] It seems that Wildman was satisfied with what the Council of Officers were suggesting because he abandoned further agitation, and in the winter of 1648–49 he joined the New Model Army as major in the regiment of horse of Colonel John Reynolds.

Consequently, he was arrested on 10 February 1655 at the village of Easton, near Marlborough, Wiltshire,[17][18][19] while dictating A Declaration of the free and well-affected People of England now in Arms against the Tyrant Oliver Cromwell, esq to his secretary William Parker.

Nearly a year and a half later, on 26 June 1656 a petition begging for Wildman's release was presented to the Protector by various persons engaged in business speculations with him, and on giving security for £10,000 he was provisionally set free.

He was in frequent communication with Royalist agents, whom he contrived to persuade that he was working for the King's cause, and he signed the address presented to Charles II on behalf of the Levellers in July 1656.

Firth speculated that Wildman's political object in this complicated web of treachery was probably to overthrow Cromwell, and to set up in his place either a republic or a monarchy limited by some elaborate constitution of his own devising.

[12] In the late 1650s Wildman used his new wealth to acquire a victualing house in Bow Street, Covent Garden, at the sign of the Nonsuch, which he entrusted to his servant William Parker.

[25] In December 1659, when the Army had turned out the Long Parliament, Wildman was employed by the Council of Officers, in conjunction with Bulstrode Whitelocke, Charles Fleetwood, and others, to draw a form of government for a free state.

[26] At the same time he was plotting to overthrow the rule of the Army, and offered to raise three thousand horse if Whitelocke, who was constable of Windsor Castle, would declare for a free commonwealth.

On 28 December 1659 the House promised that the good service of those who had assisted Ingoldsby should be duly rewarded,[27] At the Restoration of the English Monarchy information against Wildman was presented to Parliament, but thanks to these recent exploits and to his hostility to Cromwell, he escaped untroubled.

Wildman was closely associated with Algernon Sidney, both of whom were distrusted by the leaders of the Scottish malcontents, and by the English noblemen concerned, as too republican in their aims.

Wildman drew up a manifesto to be published at the time of the intended insurrection, and, though not one of the "public managers", was privately consulted upon all occasions and applied unto as their "chief oracle";[37] He was also credited with suggesting the assassination of the King and the Duke of York, "whom he expressed by the name of stags that would not be impaled, but leapt over all the fences which the care and wisdom of the authors of the constitution had made to restrain them from committing spoils".

[38] On 26 June 1683 he was committed to the Tower of London for complicity in the Rye House Plot, but allowed out on bail on 24 November following, and finally discharged on 12 February 1684.

[39] The chief witness against him was Lord Howard, who testified that Wildman undertook to furnish the rebels with some guns, which the discovery of two small field-pieces at his house seemed to confirm.

He was dissatisfied with the declaration published by the William, Prince of Orange to justify his expedition, regarding it as designed to conciliate the church party in England, and desiring to make it a comprehensive impeachment of the misgovernment of Charles and James.

He wrote many anonymous pamphlets on the crisis, sat in the Convention Parliament called in January 1689 as member for Wootton Bassett and was a frequent speaker.

[44] In the proceedings against Burton and Graham, charged with subornation of evidence in the state trials of the late reign, Wildman was particularly active, bringing in the report of the committee appointed to investigate the case, and representing the Commons at a conference with the House of Lords on the subject.

[46] But before long strong complaints were made that he was using his position to discredit the Tory adherents of William III by fictitious letters which he pretended to have intercepted; and there were also reports that he was intriguing with Jacobite emissaries.