She was born Charlotte Boyle-Walsingham in Castlemartyr, County Cork, Ireland or in London, where she died.

(Her mother, the second daughter of Frances Coningsby, had bought this estate in 1784 from Lord Hertford, who was grieving the death of his wife there two years earlier.)

In London on 3/4 August 1791, more than a year after her mother's death, Charlotte married Lord Henry FitzGerald, a member of the Duke of Leinster's family.

Charlotte was frequently pregnant during her marriage, giving birth to thirteen children in twenty-one years, of which nine survived to adulthood: After petitioning King George III in 1790, she was eventually (in 1806) able to end the abeyance to the Barony of de Ros, the most ancient baronial title in England, in her favour — even though there were two other co-heirs to the barony, and she had only a quarter interest; another claimant, Sir Henry Hunloke, 4th Bt., had a half interest and was the heir general of the elder of the two sisters from whom the claims were derived.

No clear explanation for the award was given by the House of Lords except an inference that Charlotte came from (or at least had married into) a better family.