In 1781, Onslow was involved in a homosexual scandal, and was forced to resign his seat in Parliament (by accepting the Stewardship of East Hendred) and flee to France.
[2] Onslow was educated at Christ Church, Oxford, matriculating in 1774.
He briefly sat as Member of Parliament for Aldborough in 1780 and was elected the same year as a fellow of the Royal Society.
Their son Maurice was the father of the French genre painter Édouard Onslow (1830-1904).
[4] Marie was possessed of a considerable dowry, and Onslow spent the rest of his life as a country gentleman in France.