He is often credited with inventing "Parliamentary management", the first conscious effort to convert a mass of country backbenchers into an organised Government lobby.

[4] In 1673 Osborne opposed Charles II's Royal Declaration of Indulgence, supported the Test Act, and spoke against the proposal for giving relief to the dissenters.

In June 1675 he signed the paper of advice drawn up by the bishops for the king, urging the rigid enforcement of the laws against the Roman Catholics, their complete banishment from the court, and the suppression of conventicles.

[5] A bill introduced by him imposing special taxes on recusants and subjecting Roman Catholic priests to imprisonment for life was only thrown out as too lenient because it secured offenders from the charge of treason.

The same year he introduced a Test Oath by which all holding office or seats in either House of Parliament were to declare resistance to the royal power a crime, and promise to abstain from all attempts to alter the government of either church or state; but this extreme measure of retrograde toryism was rejected.

In 1677, to secure Protestantism in case of a Roman Catholic succession, he introduced a bill by which ecclesiastical patronage and the care of the royal children were entrusted to the bishops; but this measure, like the other, was thrown out.

As he wrote in a memorandum in the summer of 1677, an English Minister must consider only how England's interests stand, and all considerations including trade, religion, and public opinion pointed to the Dutch Republic, not France, as the desired ally.

In 1677, after two years of tedious negotiations, he overcame all obstacles, and in spite of James's opposition, and without the knowledge of Louis XIV, effected the marriage between William and Mary that was the germ of the Revolution and the Act of Settlement.

[8] Simultaneously with negotiating the royal policy of an Anglo-French alliance, Danby guided through parliament a bill for raising money for a war against France; a league was concluded with the Dutch Republic, and troops were actually sent there.

That Danby, in spite of his compromising transactions on the King's behalf, remained in intention faithful to the national interests, appears clear from the hostility with which he was still regarded by France.

In 1676, Ruvigny described Danby to Louis XIV as intensely antagonistic to France and French interests, and as doing his utmost to prevent the treaty of that year.

Although both abroad and at home his policy had generally embodied the wishes of the ascendant party in the state, Danby had never obtained the confidence of the nation.

[11] The Earl of Shaftesbury, doubtless no friendly witness, spoke of him as an inveterate liar, "proud, ambitious, revengeful, false, prodigal and covetous to the highest degree",[13] and Burnet supported his unfavourable judgment.

His corruption, his submission to a tyrannical wife, his greed, his pale face and lean person, which had replaced the handsome features and comeliness of earlier days, were the subject of ridicule, from the witty sneers of Halifax to the coarse jests of the anonymous writers of innumerable lampoons.

He immediately went over to the opposition, and in concert with Louis XIV and Paul Barillon, the French ambassador, who supplied him with a large sum of money, arranged a plan for effecting Danby's ruin.

[11] He was voted guilty by the Commons; but while the Lords were disputing whether the accused peer should have bail, and whether the charges amounted to more than a misdemeanour, Parliament was prorogued on 30 December and dissolved three weeks later.

In March 1679, a new Parliament hostile to Danby was returned, and he was forced to resign the treasurership; but he received a pardon from the king under the Great Seal, and a warrant for a marquessate.

[16] His proposed advancement in rank was severely reflected upon in the Lords, Halifax declaring it in the king's presence the recompense of treason, "not to be borne".

A number of pamphlets asserting his complicity in the Popish Plot, and even accusing him of the murder of Sir Edmund Berry Godfrey, were published in 1679 and 1680; they were answered by Danby's secretary, Edward Christian in Reflections.

For some time all appeals to the king, to Parliament, and to the courts were unavailing; but on 12 February 1684 his application to Chief Justice Jeffreys was successful, and he was set at liberty on bail of £40,000, to appear in the House of Lords in the following session.

[11] Following the accession of James II, Danby was discharged from his bail by the Lords on 19 May 1685, and the order declaring dissolution of Parliament not to be abatement of impeachment was reversed.

He appears to have thought that William would not claim the crown,[17] and at first supported the theory that as the throne had been vacated by James's flight, the succession fell to Mary.

This met with little support and was rejected both by William and by Mary herself, so he voted against the regency and joined with Halifax and the Commons in declaring the prince and princess joint sovereigns.

The antagonism between the "black" and the "white" marquess (the latter being the nickname given to Carmarthen in allusion to his sickly appearance),[19] which had been forgotten in their common hatred to the French and to Rome, revived in all its bitterness.

[19] In Queen Anne's reign, in his old age, the Duke of Leeds was described as "a gentleman of admirable natural parts, great knowledge and experience in the affairs of his own country, but of no reputation with any party.

He had purchased the Harthill estate while Earl of Danby, and had a fine mortuary chapel built in the north-east corner of All Hallows Church.

[25] Leeds's estates and titles passed to eldest surviving son and heir Peregrine (1659–1729), who had been in the house of Lords as Baron Osborne since 1690, but is best remembered as a naval officer in the Royal Navy, where he rose to the rank of vice admiral.