Paramedics pronounced him dead at 9 a.m., said Craig Harvey, chief investigator for the Los Angeles County coroner's office. The cause of death was not immediately determined, Harvey said, but an autopsy could be conducted as early as Wednesday.
Renfro had reportedly been drinking with friends the evening before his death, Harvey said.
Renfro's lawyer, Richard Kaplan, said he did not know whether the death was connected to any problems with addiction.
"He was working hard on his sobriety," Kaplan said. "He was doing well. He was a nice person."
Renfro recently completed a role in "The Informers," a film adaptation of a Bret Easton Ellis novel that stars Winona Ryder, Brandon Routh and Billy Bob Thornton.
"Brad was an exceptionally talented young actor and our time spent with him was thoroughly enjoyable," Marco Weber, president of the film's production house, Senator Entertainment, said in a statement.
The actor served 10 days in jail in May 2006 after pleading no contest to driving while intoxicated and guilty to attempted possession of heroin.
The latter charge stemmed from his arrest in Los Angeles' Skid Row area, when he attempted to buy heroin from an undercover officer in 2005.
For several years he was better known for that drug bust and the resulting criminal case than for acting.
After one court appearance, he talked to reporters about drug rehabilitation, saying he was "tired of paying the consequences" for drinking and drug use and eager to get clean.
"It's definitely been an eye-opener," he said of his rehabilitation program.
Other run-ins with the law included a 1998 charge of cocaine and marijuana possession, for which he avoided jail time in a plea deal. He was also placed on probation in January 2001 and ordered to pay $4,000 for repairs to a 45-foot yacht he and a friend tried to steal in Florida in August 2000.
He was arrested again in May 2001 and charged with underage drinking, violating the terms of his probation, and was ordered into alcohol rehabilitation the following March.
A native of Knoxville, Tenn., Renfro's film career began when he was 12, acting opposite Susan Sarandon and Tommy Lee Jones in "The Client." His other credits included "Sleepers," "Deuces Wild," "Apt Pupil" and "The Jacket."