In 1969 he co-founded AUM, the first state-approved school of esoteric studies in the country which granted certificates in the occult sciences, mystic arts and religious metaphysics.

In 1981, Hieronimus was awarded a Ph.D. from Saybrook Graduate School for his doctoral thesis, "An Historic Analysis of the Reverse of the American Great Seal and Its Relationship to the Ideology of Humanistic Psychology."

His occult and symbolic murals include the 2,700-square-foot (250 m2) prophetic Apocalypse completed during 1968–1969 at the Johns Hopkins University, which led to Hieronimus being called "one of this country's best muralists".

Art historian and critic Alan Barnet noted, "Hieronimus has a talent for winning the cooperation of the establishment while he lives and works in the counter-culture."

His Independence Hall speech on the Great Seal's bicentennial was published in the Congressional Record (1983, 1984), and his research was shared in a personal meeting with the late Egyptian President Anwar El-Sadat.

Inner Traditions published a popular version of Hieronimus's doctoral thesis in 1989, entitled America's Secret Destiny: Spiritual Vision and the Founding of a Nation.

Spray Filmes was hired by Volkswagen in Brazil and the PR firm ALMA BBDO to create and present awards to people around the world that they determined had the most touching stories related to the classic VW Kombi bus.

Hieronimus has been a frequent guest on radio and television talk shows across the country since 1967 sharing his research in metaphysical symbolism, the founding fathers, America's Great Seal, UFOs and the paranormal, and even synchronistic methods for picking winning lottery numbers.

In 1990 Hieronimus & Co., Inc. was incorporated to serve as a media research service, providing story and guest ideas and materials to television, newspapers and radio worldwide.