A native New Yorker who began his career at age 16, drawing comic books and hundreds of magazine and book illustrations, as well as covers for paperback books. As one of the "golden age" era of comic book artists, his illustrations for magazines (including The Shadow and Doc Savage) have influenced the pop art school. He studied at the Art Students League, where he later taught from 1969 to 1974. Kinstler ultimately made the transition to portraitist, and established himself as one of the nation's foremost portrait painters. For over forty years, Kinstler has also devoted time to landscapes and watercolors.

In 1999, Kinstler received the Copley Medal from the Smithsonian, National Portrait Gallery, its highest honor. in 2001 Kinstler received the Portrait Society of America’s Gold Medal Award, also its highest honor.