Baron Greenwich was a title in the Peerage of the United Kingdom that has been created twice in British history.

Prior to the title's first creation in the Peerage of Great Britain in 1767, King Charles II of England planned to create the title "Countess of Greenwich" for Nell Gwyn, one of his low-born mistresses. This was to follow Charles II bestowing the titles of Duchess of Cleveland, Countess of Castlemaine, Baroness Limerick, and Baroness Nonsuch upon his other mistress, Barbara Palmer; the title of Viscountess Shannon upon his first mistress, Elizabeth Killigrew; and the titles of Duchess of Portsmouth, Duchess of Aubigny, Countess of Fareham, and Baroness Petersfield to yet another mistress, Louise de Kérouaille.

However, Charles died on 6 February 1685, having never followed through on his original plans to ennoble Gwyn.^[2]

The first official creation came in the Peerage of Great Britain in 1767, when Lady Caroline Townshend was made Baroness Greenwich, in the County of Kent, with remainder to the male issue by her second husband, Charles Townshend. She was the daughter of Field Marshal The 2nd Duke of Argyll, who had been created Earl of Greenwich in 1715 and Duke of Greenwich in 1719, titles which became extinct on his death in 1743. As Caroline's two sons by her second husband predeceased her, the title became extinct upon her death in 1794.

The second creation came in the Peerage of the United Kingdom in 1947 when Lieutenant Philip Mountbatten, on the morning of his wedding to Princess Elizabeth (who became Queen Elizabeth II), was made Baron Greenwich, of Greenwich in the County of London. He was made Duke of Edinburgh and Earl of Merioneth at the same time.^[3] Prince Philip died in 2021, and the title passed to his son Prince Charles, until it merged with the crown when Charles became King in 2022.

• Caroline Townshend, 1st Baroness Greenwich (1717–1794)

• Prince Philip, Duke of Edinburgh (1921–2021), 1st Baron Greenwich.
• Charles, Prince of Wales (b. 1948), 2nd Baron, eldest son of Prince Philip, Duke of Edinburgh.
  • Prince Charles succeeded as Charles III in 2022 upon his mother's death, and his hereditary titles merged in the Crown.