English statesman, lord treasurer in Charles II's Cabal ministry.

Clifford matriculated at Exeter College, Oxford, in 1647 and entered the Middle Temple in 1648. In Parliament in 1660–61 he became a steady supporter of Henry Bennett (who became Lord Arlington in 1665) in opposition to the chancellor, the Earl of Clarendon. Knighted in 1664 and appointed ambassador to Denmark and Sweden, he served with the fleet in 1665 and 1666. In 1666 he was made controller of the household and a privy councillor, in 1667 a commissioner for the treasury, and in 1668 treasurer of the household.

As one of the Cabal ministry, Clifford cooperated zealously with the King in breaking through the triple alliance with the United Provinces and Sweden and in effecting an understanding with France. He was the only minister, besides Arlington, entrusted with the secret Treaty of Dover of 1670; he signed it as well as the ostensible treaty shown to all the members of the Cabal. In 1672, during the absence abroad of Arlington and Sir William Coventry, Clifford acted as principal secretary of state. In the same year he was appointed a commissioner to inquire into the settlement of Ireland. On April 22, 1672, he was raised to the peerage and, on November 28, by the Duke of York's interest, was made lord treasurer. This excited the jealousy of Arlington, who had always aspired to that office. It was, however, the Test Act of 1673 which brought about Clifford's downfall. On the passing of the bill Clifford followed the Duke of York into retirement. He had, it would seem, been gradually moving toward Roman Catholicism, and probably the Test Act precipitated his conversion to the Roman faith. He gave up the treasurership and his seat in the privy council in June. He left London for his Devon estate, and his death a few months later may have been a suicide.