The son of William Warner and Margaret Thompson Warner, Cheiro was born William John Warner in the village of Rathdown, outside Dublin, Ireland. He took the name Count Louis Hamon (or Count Leigh de Hamong).As mentioned in his memoirs, Cheiro acquired his expertise in India. As a teenager, he travelled to the Bombay port of Apollo Bunder. There, he met his guru, an Indian Chitpavan Brahmin, who took him to his village in the valley of the Konkan region of Maharashtra. Later Cheiro was permitted by Brahmans to study an ancient book that has many studies on hands. After studying thoroughly for two years, he returned to London and started his career as a palmist.Cheiro was reluctant to marry but was aware that he was destined to marry late in life.

This did happen after a woman took care of him during a serious illness. A separate chapter is devoted to this matter in his memoirs.