Thomson was born in Des Moines, Iowa. In his youth, he performed in bands such as Body Pit. Thomson joined Slipknot in 1996, replacing the band's guitarist, Craig Jones, who then begun to assume his role as their sampler. He employs alternate picking, drop tuning, and 6 string sweep arpeggios into his guitar technique.

Thomson expresses his pseudonym as #7 more than most members of Slipknot. For example, as well as being credited with the number in the liner notes of albums he has recorded, he also has the word "seven" tattooed on his left arm, and features the number "7" on the designs of at least three guitar models he has used. Outside Slipknot, Thomson has taught guitar lessons at Ye Olde Guitar Shoppe, a local music shop in Des Moines, and has appeared on Malevolent Creation's album Doomsday X. He also made a guest appearance in the music video for Lupara's "No Pity on the Ants".

According to Slipknot vocalist Corey Taylor, Thomson is an avid writer of poetry, loves cats, and has a fascination with serial killers. On the topic of the latter, Thomson himself has stated, "If I were a famous killer, I'd take some of the finer points of quite a few of them- Albert Fish and Ed Gein spring to mind. But I'm not a violent person by nature. Don't fuck with me, and you'll be fine." ^[2]

Mick has a number of tattoos on his body: he has the word "嫌惡" on his right arm (which means "detest" and "disgust" in Mandarin and "HATE" in Japanese), the word "Seven" on his left forearm, a "demon attempting to rape an angel" on his shoulder (actually artwork from Immolation's first album Dawn of Possession), on his other shoulder a morbid angel tattoo by paul booth, an inverted cross on his upper back, "Slipknot" going down his right calf, and the Zodiac sign for Scorpio on his left calf. Mick is 6'2" and 242 pounds, being the 2nd tallest member of Slipknot, behind fellow guitarist Jim Root, and the heaviest.