Hercule Mériadec de Rohan (13 November 1688 – 21 December 1757) was a prince étranger and the sixth Duke of Montbazon in France, "Prince de Guéméne" being the title he bore prior to inheriting the dukedom.

Born to Charles de Rohan and his wife, Charlotte Élisabeth de Cochefilet, he was the couple’s third child and second son. Until the death of his paternal grandfather, Charles, 4th Duc de Montbazon in 1699, he was fifth in line of succession to the dukedom and not expected to inherit it: Ahead of him were his father Charles, then styled Prince de Guéméné (1655-1727), his eldest brother François-Armand, Prince de Montbazon (1682-1717), François-Armand's son Charles-Jules de Rohan (1700-1703) and another older brother, Louis-Charles-Casimir, Comte de Rochefort (1686-1749). After Charles-Jules died as a child, Louis-Charles-Casimir forfeited his claim to a secular inheritance by joining the Order of the Holy Cross, whereupon Hercule Mériadec became Comte de Rochefort. His father was the fifth Duc de Montbazon, but succession to that title remained uncertain until François-Armand died without living children at the age of 35 in 1717, leaving Hercule-Mériadec to become Prince de Guéméné, the title usually borne by the heir apparent.

Only when his father died in October 1727 did he succeed to the Montbazon ducal peerage and become head of the House of Rohan, which enjoyed the high rank of princes étrangers at the court of Louis XVI.

While serving in the Gendarmes de la Garde, he held the position of standard-bearer of the company.

Hercule Mériadec's siblings included Louis Constantin de Rohan, Bishop of Strasbourg, and Armand Jules de Rohan-Guéméné, Archbishop of Rheims, who crowned Louis XV king.

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