Root was born in Des Moines, Iowa. He has performed in bands such as Anal Blast, Atomic Opera, Deadfront and Stone Sour; the latter which he joined in 1995, and returned to along with vocalist Corey Taylor, during its revival in 2002. Prior to joining Slipknot, he worked as a screenprinter, waiter, and busboy. Root joined the band in January 1999, replacing their original guitarist, Josh Brainard, who left the band during the recording of their self-titled album, reportedly after having fulfilled his recording duties. In fact, the only two songs Root recorded during the album's sessions was "Purity" and "Me Inside", the former being featured only on the short-lived first pressing of Slipknot and the latter being its replacement. Despite this, the song has become a staple for the band's live performances. Slipknot vocalist Corey Taylor invited Root to join the band based on Taylor's past experiences working with him in Stone Sour, before leaving the band to join Slipknot.

As well as lending his guitar talents to Stone Sour, Root has also performed drums on one song the band has recorded, the Come What(ever) May bonus track "The Day I Let Go". Outside Slipknot and Stone Sour, Root has appeared on Slipknot turntablist Sid Wilson's DJ Starscream album The New Leader and John 5's The Devil Knows My Name, and also appeared on the Roadrunner United project, performing the solo and harmony guitars on "Tired 'N Lonely" from the project's album The All-Star Sessions. He also appeared on Jonathan Davis and the SFA´s cover of Lil Wayne´s "Got Money".

Jim Root has been dating Cristina Scabbia of Lacuna Coil since 2004 when they met at Ozzfest.