Charles Lennox, 3rd Duke of Richmond and Lennox (1733 - December 1806), was one of the most remarkable men of the 18th century, being chiefly famous for his advanced views on the question of parliamentary reform.

Charles Lennox succeeded his father to the peerage in 1750. He had many sisters, including the Ladies Caroline Lennox, Emily Lennox, Louisa Lennox and Sarah Lennox.

He was appointed British ambassador extraordinary in Paris in 1765, and in the following year he became a secretary of state in the Rockingham administration, resigning office on the accession to power of the Earl of Chatham.

In the debates on the policy that led to the War of American Independence Richmond was a firm supporter of the colonists; and he initiated the debate in 1778 calling for the removal of the troops from America, during which Chatham was seized by his fatal illness. He also advocated a policy of concession in Ireland, with reference to which he originated the phrase "a union of hearts" which long afterwards became famous when his use of it had been forgotten. In 1779 the duke brought forward a motion for retrenchment of the civil list; and in 1780 he embodied in a bill his proposals for parliamentary reform, which included manhood suffrage, annual parliaments and equal electoral areas.

Richmond sat in Rockingham's second cabinet as Master-General of the Ordnance; and in 1784 he joined the ministry of William Pitt. He now developed strongly Tory opinions, and his alleged desertion of the cause of reform led to a violent attack on him by Lauderdale in 1792, which nearly led to a duel between the two noblemen. Richmond died in December 1806, and, leaving no legitimate children, he was succeeded in the peerage by his nephew Charles, son of his brother, General Lord George Henry Lennox.

|- style="text-align: center;" | width="30%" |Preceded by:
The Viscount Townshend | width="40%" style="text-align: center;" |Master-General of the Ordnance
1782–1783 | width="30%" |Succeeded by:
The Viscount Townshend

|- style="text-align: center;" | width="30%" |Preceded by:
The Viscount Townshend | width="40%" style="text-align: center;" |Master-General of the Ordnance
1784–1795 | width="30%" |Succeeded by:
The Marquess Cornwallis