Dunn was born in Taiwan, and grew up in Taiwan, Kentucky, and San Antonio, Texas, where he graduated from Central Catholic Marianist High School. It was in Taiwan that he was first exposed to Japanese manga.
In 1984 he co-founded Antarctic Press, an American comic book company specializing in manga-style (Amerimanga) titles. His most notable creations for Antarctic are the comic book series Ninja High School and Warrior Nun Areala.
In 2003, Dunn sold his portion of Antarctic Press to start his own development company, Sentai Studios. After a couple of years he closed Sentai and returned to Antarctic.
Dunn was one of the primary artists involved in the short-lived Marvel Mangaverse project. He also worked as an animator for the science-fiction film A Scanner Darkly.
In 2016, Art Greenhaw began creating, editing and writing faith-based visual novels and comic books, starting with the book series God's Silver Soldiers, also known as Silver Soldiers: The Comic and followed by Tales of Nazareth: The Boyhood of Jesus. The comic books, under the imprint of Truthmonger Comics Group Publishing, have achieved acclaim for their action-oriented innovation in illustrations by Dunn, as well as their storylines, and they have been covered in the media by TV channels, newspapers, and faith-based, nationally syndicated radio.
In 2019, Dunn created the Coalition of Independent Comic Publishers.