Darby Costello studied psychology, philosophy and theology in America in the mid 1960s. After some travel she returned to the US to study astrology in Boston, first with Francis Sarkoian and Louis Acker and then with Isobel Hickey. In 1971 she went to South Africa for a brief visit and stayed twelve years. During that time she worked with the Museum of Man and Science, in Johannesburg, recording the art and practices of the samgomas; the diviner/healers of Southern Africa. Concurrently she began doing charts for people, gradually developing a wide clientele over the years. In 1983 she came to London. During the first few years she developed her practice and began giving workshops and seminars to various groups, while deepening her own knowledge of astrology's cultural history. In 1988 she joined the Centre for Psychological Astrology where she has been teaching and supervising students ever since.
She is also a visiting tutor for the Faculty of Astrological Studies and teaches and lectures regularly throughout the UK and Europe. She wrote her first book, Astrology, for Dorling Kindersley's "Pocket" series, with Lindsay Radermacher. She then wrote three books of seminar collections for the CPA Press: The Astrological Moon, Water and Fire, and Earth and Air.
She was one of the four contributors to the The Mars Quartet, published in 2001. She received her Master's Degree in Cultural Astronomy and Astrology from Bath Spa University in 2007.