The collaboration ran from 1938 to 1943, with Harris producing multiple painted versions of several cards as Crowley refined his symbolic requirements, a process both later described as exhausting and occasionally acrimonious but never abandoned. Harris brought to the work her own serious study of projective geometry, color theory and the mathematics of perspective, and the finished cards are visually far denser and more abstract than any earlier tarot deck, layering geometric structure, alchemical and astrological symbolism and vivid color relationships that were substantially her own contribution rather than simply an illustrator's rendering of Crowley's instructions.
Neither Harris nor Crowley lived to see the project reach a wide public in finished form: Crowley's accompanying text, The Book of Thoth, was published in 1944 in a limited edition of two hundred copies, and Harris herself died in 1962 while traveling in Srinagar, in Kashmir, with the deck itself still unpublished as a standalone product; it did not reach general publication until 1969. Since then the Thoth Tarot has become one of the most widely used and imitated tarot decks in print, and Harris's original paintings, preserved at the Warburg Institute in London, are now recognized as a major work of twentieth century occult art in their own right rather than simply an accompaniment to Crowley's text.