Thomas is a second generation Montanan. After completing his college education at the University of Montana in Missoula he moved to San Francisco. He began his career in 1972 as a hand colorist for a book entitled "Historic Lithographs of San Franciso", with Burger & Evans who specialized in paintings & manuscripts of the United States. By 1974 Minckler returned to Montana and started his own business grounded in his
passion for the American West and specializing in art, rare books, documents
and vintage photography.
Thomas opened a gallery in 1979 in Billings, Montana and after 23 years, he decided to become a private art dealer with locations both in Billings and New York City. He was a board member of the J.K. Ralston Museum and remains a member of the Yellowstone Corral of Westerners.