Harwell, 56, has reached the final stage of liver failure, the report says. He had been battling medical complications for years, including issues with alcohol.
Harwell has origins in the Bay Area. Smash Mouth was formed in the 1990s out of San Jose.
Harwell announced his retirement in 2021 after a New York performance in which he was seen slurring his words, according to TMZ.
Smash Mouth is best known for its hits in the early 2000s, such as “All Star” and “I’m A Believer.” Both songs gained popularity after being featured in the 2001 film “Shrek.”