Charles Montagu was born in Horton, Northamptonshire, the son of George Montagu, fifth son of 1st Earl of Manchester. He was educated first in the country, and then at Westminster, where he was chosen as a Queen's Scholar in 1677, and entered into close friendship with George Stepney.
Montagu was admitted to Trinity College, Cambridge in 1679, graduated MA in 1682, and became a Fellow of Trinity in 1683. Two portraits of Montagu by Godfrey Kneller are in the college collection.
His relation, Dr. John Montagu, was then Master of Trinity College, and took him under his wing. At Cambridge he began a lasting association with Isaac Newton.
In 1685, Montagu's verses on the death of King Charles II made such an impression on the Earl of Dorset that he was invited to town and introduced to other entertainments. In 1687, Montagu joined with Matthew Prior in "The City Mouse and the Country Mouse," a burlesque of John Dryden's The Hind and the Panther. He sat in the Convention Parliament of 1689. At about the same time he married the Countess Dowager of Manchester, and intended taking Holy Orders, but changed his mind and purchased for £1,500 a position as Clerk of the Council.
In 1691, having become a member of the House of Commons, he argued in favour of a law to grant the assistance of counsel in trials for high treason. He became flustered in the middle of his speech, and upon recovering himself, observed "how reasonable it was to allow counsel to men called as criminals before a court of justice, when it appeared how much the presence of that assembly could disconcert one of their own body".
After the House of Commons he rose quickly, becoming one of the Commissioners of the Treasury and a member of the Privy Council. In 1694 he became Chancellor of the Exchequer, in reward for having devised the establishment of the Bank of England, the plan which had been proposed by William Patterson three years before, but not acted upon. In 1695 was involved in the successful recoinage project. In 1698, having been appointed to the first Commission of the Treasury, he was also one of the regency in the King's absence. The next year he was made Auditor of the Exchequer, and the year after created Baron Halifax, of Halifax in the County of Yorkshire, with remainder to his nephew George Montagu. His impeachment by the Commons failed, when the Articles were dismissed by the House of Lords.
John Macky, relates a short description of the circumstances leading up to Charles, Lord Halifax's impeachment, in the Secret Service Papers published by his son in 1733.
...But as all courtiers, who rise too quick, as he did, are envied, so his great Favour with the King, and powerful Interest in the House, raised a great Party against him, which he strengthened, by seeming to despise them. The Deficiency of Parliamentary Funds, and the growing Debts of the Nation, by the great Interest of Paper Credit, laid him but too much open to these Attacks, he having the whole Administration of the Revenue. When he saw the Party growing too strong for him in the House of Commons, he prudently got himself made a Lord; and as a Screen from all Objections against his Administration, quitted his Management of Commissioner, to serve as Auditor: But his Enemies did not quit him so, they followed him into the House of Peers with an Impeachment, and so left no Stone unturned, to get him out of his Employ, bespattering him every Day with Pamphlets.
—Memoirs of the Secret Services of John Macky Esq.
, pp. 51–54
On the accession of Queen Anne, Montagu was dismissed from the Council, and in the first Parliament of her reign was again attacked by the Commons, and again escaped by the protection of the Lords. In 1704 he wrote an answer to Bromley's speech against occasional conformity. He headed the inquiry into the danger of the Church. In 1706 he proposed and negotiated the Union with Scotland and when the Elector of Hanover received the Garter, after the Act had passed for securing the Protestant Succession, he was appointed to carry the ensigns of the Order to the Electoral Court. He sat as one of the judges of Henry Sacheverell, but voted for a mild sentence. Being now no longer in favour, he obtained a writ for summoning the Electoral Prince to Parliament as Duke of Cambridge.
At the Queen's death Montagu was again appointed one of the regents. At the accession of George I, he was made Viscount Sunbury and Earl of Halifax, with remainder to heirs male, a Knight of the Garter, and First Lord of the Treasury, with a grant to his nephew of the reversion of the Auditorship of the Exchequer. Shortly afterwards he died of an inflammation of his lungs. The viscountcy and earldom became extinct on his death as he had no sons while he was succeeded in the barony according to the special remainder by his nephew George Montagu.
Halifax is reported to have left Catherine Barton, Newton's niece, a sizable inheritance for "her excellent conversation", as John Flamsteed wryly reported at the time.
Alexander Pope commemorated the Earl's death in his unpublished poem "Farewell to London in the Year 1715":