It is unusual to combine mysticism and psychoanalysis. Marion Milner, however, achieved precisely this. Through her self-analysis and analytic work with children and adults—and using as an illustration her own and others’ imaginative ideas, paintings, doodles, drawings and pictures—she drew attention to the potential for health and creativity of undoing the obstacles to mystical experience of oneness with what is beyond or other than the self, which she sometimes called God, the unconscious or the id. This article seeks to explain and highlight this aspect of her contribution to, and continuing importance for, psychoanalytic theory and practice—particularly that associated with Winnicott—through detailing her early life and diary-keeping experiments, some of her psychoanalytic case histories during and after the Second World War, her work as an artist, ending with her travels and her involvement during the 1980s and 1990s with the Squiggle Foundation and British Association of Art Therapists.