Lady Charlotte was born into the English aristocracy. When she was 20 years old, she fell in love and married a budding industrialist called Josiah John Guest who was 27 years her senior. Guest was part of a new breed of 19th-century entrepreneur intent on harnessing nature for personal fortune and for the advancement of modern society. In 1815 he had taken over the Dowlais Ironworks near Merthyr Tydfil from his father.
She was a passionate humanitarian, an early environmentalist and an afficionado of the Welsh language and its literary heritage. She learned Welsh upon moving to Dowlais and soon was introduced to the Four Branches of the Mabinogi by her friend and fellow member of the Abergavenny Literary Society, John Jones (who was known by his Welsh pen name, Tegid.) In 1837, Tegid lent her a copy of the Red Book for Hergest that he had been commissioned to recreate when studying at Oxford. Lady Charlotte set about translating into English not just the Red Book of Hergest but also a series of other important Welsh poems and romances – many emboldening the legend of King Arthur. The result was The Mabinogian, published in seven volumes between 1838 and 1845.