In addition to his work with Three Days Grace and Saint Asonia, he has been involved in collaborations with other bands including Art of Dying, Apocalyptica, Breaking Benjamin, Skillet and Thousand Foot Krutch.

[8][9] Shortly after his parents divorced, he moved back to the Peterborough area, where he initially attended Adam Scott Collegiate and Vocational Institute.

"[13] Gontier's influences include Pearl Jam,[12][14] Alice in Chains,[14] Jeff Buckley,[12] Soundgarden, the Tragically Hip, and Finger Eleven.

[14] Gontier, along with Sanderson, Walst, Phil Crowe, and Joe Grant,[15] started out as "Groundswell" in Norwood, Ontario, in 1992, while attending high school.

On October 3, 2024, Three Days Grace confirmed Gontier’s official return (with Walst also remaining as a singer) and was in the studio recording new music with the band.

[24] Gontier joined singer and songwriter Martin Sexton on the road during his 2012 "Fall Like Rain" tour, providing opening support as a solo artist.

[4] In April 2014, Gontier and Staind guitarist Mike Mushok began writing songs together, without the intention of creating a band.

[27] The duo later enlisted former Finger Eleven drummer Rich Beddoe, and former Dark New Day bassist Corey Lowery to complete their lineup.

Some of his collaborations include Daughtry, Ian Thornley, Max Martin, Shaun Morgan, Ben Burnley, Art of Dying, Before the Curtain, and fellow musician and long time friend Grainne Ryan.

[6] In 2006, Gontier was a member of the rock supergroup Big Dirty Band along with Geddy Lee, Alex Lifeson, Jeff Burrows, Ian Thornley and Care Failure, covering "I Fought the Law", as part of the Trailer Park Boys movie soundtrack.

[36] Gontier was also featured on the track "Raining" by fellow Canadian band Art of Dying on their album Vices and Virtues.

[39] Gontier formed a new project called Diviidedby together with former USS MC Jason "Human Kebab" Parsons in April 2023.

Gontier was inducted into the Norwood District High School Hall of Honor in July 2022 along with Brad and Matt Walst.

[49] In 2005, Gontier went into rehabilitation at the CAMH (Centre for Addiction and Mental Health) in Toronto, where he wrote many of the songs for One-X, including "Never Too Late", which was co-written by Adam's ex-wife, Naomi Faith Brewer.