Mireault was born in Marville, France, where both parents were stationed while working for the Canadian Forces. In 1963, the Mireault family moved back to Canada. Raised as an Anglophone in Rawdon, Quebec, he has been an active participant in the Montreal underground comix scene, participating in the comix jams since their early inception and contributing to local zines and underground publications. At the same time he has worked in the mainstream comics industry as an artist and colourist, as well as an animator and illustrator.

Among his comics works are Dr. Robot, Mackenzie Queen, Bug-eyed Monster, The Blair Witch Chronicles, and Left Alone: The Rustin Parr Killings, Two Fisted Science: Safecracker, When is a Door? The Tragic Though Amusing History of Clay Face II, and the creator-owned comic The Jam, published on and off from 1987 by various companies including Comico, Slave Labor Graphics, Tundra Publishing, Dark Horse Comics, and Caliber Press.

Mireault also served as the artist on the story arc The Devil Within for Matt Wagner's Grendel comics in the late 1980s — notably coloured by Joe Matt. Mireault also coloured several Grendel story arcs: Warchild, Devil's Hammer, Devil in Our Midst, Devil Tracks, Devil Eyes, Devil by the Deed, The Devil's Apprentice.

As a colourist he has also had a long-standing collaborative relationship with Salgood Sam a.k.a. Max Douglas, a fellow Canadian artist. Together they worked on Wonder Woman Vs. the Red Menace, Muties #6: The Patriot Game, and Revolution on the Planet of the Apes.

Another long-standing collaborative relationship has been with Mike Allred, with whom he’s produced Madman Jam: The Fall of the House of Escher, Creatures of the Id, and The Everyman. And Mireault’s character Dr. Robot first appeared as a back-up in the back of Mike Allred’s Madman.

Mireault also has a part-time band called Bug-Eyed Monster, for which he writes the occasional song.