The FOI was founded at Huntington Castle, Co. Carlow, Ireland at the Vernal equinox of 1976. The three co-founders were Olivia Robertson and her brother, Lawrence Durdin-Robertson (grandchildren of Thomas Herbert Robertson) and Lawrence's wife Pamela. Their aim was to create a fellowship to "help the Goddess actively in the manifestation of Her divine plan." Olivia has described Isis as "God in female form." The FOI grew out of a "working group" created in 1963 called the Huntington Castle Centre for Meditation and Study. This Centre was active in gathering together various occult and theological figures such as Ross Nichols, Josephine and Mohun Lall, and Gerald Gough. The experiences shared within this group, along with the personal spiritual revelations and experiences of the three FOI co-founders led to the eventual founding of the Fellowship of Isis on the Vernal Equinox, 1976. From 1976 until the early 1990s, the group steadily grew.