Leonowens served at court until 1867, a period of nearly six years, first as a teacher and later as language secretary for the king. Although her position carried great respect and even a degree of political influence, she did not find the terms and conditions of her employment to her satisfaction, and came to be regarded by the king himself as a rather difficult woman.

In 1868 Leonowens was on leave for her health in England and had been negotiating a return to the court on better terms when Mongkut fell ill and died. The king mentioned Leonowens and her son in his will, though they did not receive the legacy. The new monarch, fifteen-year-old Chulalongkorn, who succeeded his father, wrote Leonowens a warm letter of thanks for her services.

By 1869 Leonowens was in New York, and began contributing travel articles to a Boston journal, Atlantic Monthly, including ‘The Favorite of the Harem’, reviewed by the New York Times as ‘an Eastern love story, having apparently a strong basis of truth’.She expanded her articles into two volumes of memoirs, beginning with The English Governess at the Siamese Court (1870), which earned her immediate fame but also brought charges of sensationalism. In her writing she casts a critical eye over court life; the account is not always a flattering one, and has become the subject of controversy in Thailand; she has also been accused of exaggerating her influence with the king."