She is of Hungarian background and attributes a childhood spent in the culturally diverse Queens borough of New York City as a significant influence on her writing career. Illes explains that her interest in divination began while playing with a Tarot deck at the age of six. Her first Tarot deck was the Builders of the Adytum (BOTA) deck, which she described in a 2005 interview as "formidable and very esoteric," an unusual starter for a child of her age. In an interview in 2016, Illes reported that she still had the BOTA deck, which her sister had purchased for her from the Samuel Weiser Bookstore in New York City.
During her teen years, Illes frequented New York bookstores such as Magickal Childe and Samuel Weiser's, known for their metaphysical and occult collections, and Latin botanicas Her love for esoteric books led to her interest in astrology, which began with Zolar's It's All in the Stars.
She has a Bachelor of Arts in English and Communications from Rutgers College and earned a Graduate Certificate in Aromatherapy from the American College of Healthcare Sciences (previously known as the Australasian College of Health Sciences) in 1999.
Illes worked as a "telephone psychic" for Psychic Friends Network from 1991 to 1993. She went on to become a prolific author of reference books and contributed magazine articles in the ancient non-traditional arts.
Her writing interests include folklore, folkways, mythology, astrology, spellcasting, spirit-working, herbalism and traditional healing. She also covers the subjects of the occult, magic, divination, spiritualism, fairies, witchcraft and the paranormal.
A certified aromatherapy consultant, she has taught introductory courses on the subject at the Australasian College (2000–2002), and practices taromancy. Although she practices and teaches other forms of divination, she considers Tarot to be her "main practice" and has been reading Tarot cards professionally since the age of 26.
She sometimes holds workshops relating to her books or other specialized subjects. In 2012, she gave a workshop on the use of symbols as part of the SIgils & Signs Art Show at Observatory in Brooklyn. She gives similar workshops and presentations intermittently throughout the year.
The first complete book Illes wrote was about traditional methods of enhancing fertility. It contained a chapter about magic spells, which a publisher asked her to expand into a book of its own, eventually published as Pure Magic: A Complete Course in Spellcasting. The manuscript about fertility was set aside, but in a 2011 interview by The Witches' Almanac, Illes mentioned that she may eventually publish it under the title, Frogs and Pomegranates.
After the release of The Encyclopedia of 5000 Spells, her publisher suggested an encyclopedia about witchcraft. A note of encouragement from the Non-Wiccan Witches Yahoo group persuaded her to accept the challenge, which led to The Element Encyclopedia of Witchcraft. According to Illes, most encyclopedias about witchcraft were written by outsiders and "not really about witches or their craft."
Illes has been an occasional guest on George Noory's nightly radio broadcast, Coast to Coast AM, where she has discussed spellcasting, witchcraft and other occult subjects. She has also been featured as a guest on Ripley's Radio Oddcast, Fangoria Radio, the Hilly Rose Show, and Rob McConnell's "X" Zone radio show.
Her last name, Illes, is pronounced as you would with the "Ph" omitted from "Phyllis." Judith Illes was used as the byline for some of her Tour Egypt articles, rather than her Hungarian name, Judika.
In an interview with The Witches' Almanac, Illes disclosed that she used "Judith Joyce" as her byline when she wrote The Weiser Field Guide to the Paranormal due to the short period between her other Weiser field guides.