Savile sat in the Convention Parliament that restored King Charles II to the throne in 1660, and in 1668 he became Viscount Halifax. Admitted to the Privy Council in 1672, he opposed Charles's covert pro-French and pro-Roman Catholic policies. Nevertheless, he balanced this opposition by fighting the anti-Catholic Test Act of 1673. In 1676 Halifax was dismissed from the Council for repeatedly showing hostility to the King's chief minister, Thomas Osborne, earl of Danby; he regained his seat, however, in 1679 and in the same year was created marquess of Halifax. Adhering to his principles of moderation, he successfully led the fight in the House of Lords (Nov. 15, 1680) against a bill that would have excluded Charles's Roman Catholic brother James, duke of York, from succession to the throne. In October 1682 he became lord privy seal. But upon the accession of the Duke of York as James II in February 1685, Halifax was demoted to lord president of the council, from which office he was summarily dismissed on October 21. He spent the next three years writing political pamphlets. His Character of King Charles the Second was written during this period, and The Character of a Trimmer, a statement of his political creed, was published in 1688.

When James's enemy William of Orange (William III) invaded England in November 1688, Halifax tried, at the behest of James, to arrange a compromise between the two men. After he failed, he sided with William. It was largely a result of his efforts that the Convention Parliament of 1689 accepted William and Mary as joint sovereigns of England. In the new regime, Halifax was lord privy seal and chief minister of the crown until his enemies in both the Whig and Tory parties forced him to resign in February 1690.