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 and 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 York, with remainder to his nephew George Montagu. His impeachment by the Commons failed, when the Articles were dismissed by the
House of Lords.
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.