He was the eldest son of Ugo, 4th Duke of Sora and Duchess Maria Ruffo di Bagnara.
He married Giustina Gallio (29 October 1644 – 21 July 1679) and then, when she died, he married Ippolita Ludovisi on 19 October 1681.[1] The Boncompagni-Ludovisi union lasted until the French Revolution and included the development of the Archivio Boncompagni-Ludovisi held by The Vatican.[2]
Gregorio and Ippolita had six children:
- Hugo (1684–1686) died young
- Maria Eleonora (1686–1745), Princess of Piombino, married her uncle and Gregorio's brother Antonio I Boncompagni
- Constance (1687–1768), married Vincenzo Giustiniani, Prince of Bassano
- Maria Teresa (1692–1744), married Urbano Barberini, Prince of Palestrina
- Giulia (1695–1751), married Marco Ottoboni, Duke of Fiano
- Anna Maria (1696–1752), married Gian Vincenzo Salviati, Duke of Giuliano
