King, known for his hits Lucille, Sweet Black Angel and Rock Me Baby, died in his sleep in Las Vegas.
Born in Mississippi, King began performing in the 1940s and was inducted into the Blues Foundation Hall of Fame and the Rock and Roll Hall of Fame.
He was recently taken to hospital with a diabetes-related illness.
Rolling Stone magazine once ranked BB King in third place in its list of the 100 greatest guitarists of all time, just below Jimi Hendrix and Duane Allman.
A former farmhand, King was awarded his 15th Grammy award in 2009 for his album One Kind Favor.
Even until recently, King performed in at least 100 concerts a year.
The 'King of the Blues' guitarist and singer, BB King, has died aged 89, his lawyer says.