Cornell (52) was found dead in his Detroit hotel bathroom on Wednesday night (local time) after playing a concert in the city with the grunge band.
"The cause of death has been determined as suicide. A full autopsy report has not yet been completed," the the Wayne County Medical Examiner's Office said in a statement after conducting an initial autopsy.
Cornell's publicist Brian Bumbery said earlier that the singer's death was "sudden and unexpected."
Detroit police spokesman Dan Donakowski said that officers were called to Cornell's hotel around midnight by a friend of the musician and found Cornell "laying in his bathroom, unresponsive and he had passed away."
Cornell, the lead singer of Soundgarden and later Audioslave, had tweeted earlier on Wednesday: "#Detroit finally back to Rock City !!!! @soundgarden."
“What I look forward to the most -- because I tour so much, especially the last couple of years, by myself -- is the camaraderie. It’s what we missed when we weren’t a band,” Cornell had posted on Facebook on Tuesday. The band had been in the middle of a U.S. tour.
Soundgarden was one of the leading bands in the grunge music movement in the 1980s and '90s, releasing albums such as "Badmotorfinger" and the Grammy-winning "Superunknown," which brought the band mainstream music scene success.
Cornell had spoken openly in interviews of his struggles with drugs as a teenager, and later with alcohol. But he said in 2007 that he had been sober since checking himself into rehab in 2002. He also spoke of periods of depression and agoraphobia.
Led Zeppelin guitarist Jimmy Page led tributes on Thursday to Cornell, calling him on Twitter "Incredibly Talented, Incredibly Young, Incredibly Missed."
Kiss singer Paul Stanley tweeted he was "Stunned to hear the death of Chris Cornell," while Aerosmith's Joe Perry called his passing "a sad loss of a great talent to the world."
Soundgarden broke up in 1997 and Cornell in 2001 joined members of Rage Against The Machine to form Audioslave, which earned acclaim with its self-titled album.
Soundgarden reunited in 2010 and embarked on the current U.S. tour in April.
Cornell also had an extensive solo career as a singer, guitarist, composer and lyricist and worked with various other musicians over three decades in the music business.
Where to get help
• Lifeline: 0800 543 354 (available 24/7)
• Suicide Crisis Helpline: 0508 828 865 (0508 TAUTOKO) (available 24/7)
• Youthline: 0800 376 633
• Kidsline: 0800 543 754 (available 24/7)
• Whatsup: 0800 942 8787 (1pm to 11pm)
• Depression helpline: 0800 111 757 (available 24/7)
If it is an emergency and you feel like you or someone else is at risk, call 111.
