He was the couple's fourth child and had an older sister Maria Teresa and two brothers who died before his birth.

[3] In 1741, he married Maria Teresa Cybo-Malaspina, heir and, from 1780, sovereign of the Duchy of Massa and Carrara: their relations turned out to be extremely unhappy and the Duchess lived for most of the time in Reggio, separated from her husband.

Generally appreciated by his subjects (he sometimes spoke in Modenese dialect with them), Ercole continued the reform begun by his father.

After the death of his wife in 1790, he married morganatically in 1795 with his long-time mistress Chiara Marini (d. Treviso, 1800), whom he invested with title of Marchioness of Scandiano (only formally, without any authentic rule over this land).

The peaces of Treaty of Campo Formio (1797) and Lunéville had assigned him territories in Breisgau in exchange of the lost duchy, but he never took possession of them.