Harwell, who sang hits like All Star and Then the Morning Comes, suffered acute liver failure, band manager says.
The band’s manager, Robert Hayes, said Harwell “passed peacefully and comfortably” on Monday morning at his home in Boise, Idaho, where he was surrounded by family and friends.
The cause of death was acute liver failure, Hayes said in a statement.
Smash Mouth was known for hit songs including All Star and Then The Morning Comes.
“Steve Harwell was a true American Original. A larger than life character who shot up into the sky like a Roman candle,” Hayes said in the statement. “Steve should be remembered for his unwavering focus and impassioned determination to reach the heights of pop stardom.”
Born in California in 1967, Harwell performed in a rap group called F.O.S. (Freedom of Speech) before forming Smash Mouth in 1994.
The band released two platinum albums on Interscope Records: 1997’s ska-fuelled Fush Yu Mang and 1999’s Astro Lounge.
The second album featured some of the band’s biggest hits, including the Grammy-nominated, platinum single All Star, which appeared in the animated movie Shrek along with their cover of the Monkees’ song I’m a Believer.
Humour was a driving force behind Smash Mouth’s success, and at the forefront of the band’s popularity was Harwell’s playful alt-rock voice and persona. He made a cameo in 2001 comedy film Rat Race and had a well-documented friendship with the Food Network chef and host Guy Fieri.
“Steve lived a 100% full-throttle life. Burning brightly across the universe before burning out,” Hayes said, adding that the late singer had “irrepressible charm and charisma”.
“He will be greatly missed by those who knew and loved him,” he said.
Harwell left Smash Mouth in 2021, though the band continued to tour with Zach Goode as its lead singer. The band released a statement at the time saying Harwell had been diagnosed with cardiomyopathy eight years earlier and had suffered “nonstop serious medical setbacks including heart failure as well as acute Wernicke Encephalopathy”.
Hayes had released a statement on Sunday saying Harwell was in hospice care.
Harwell will be cremated in Boise and buried in San Jose, California, alongside his mother, Hayes said.