Maranhao state public safety spokeswoman Maud Zaiban said that Jose Agostinho Pereira was decapitated by fellow inmates who broke into his cell in the city of Pinheiro.
In June, Pereira was charged with imprisoning his daughter for 12 years in his home and fathering her seven children. Prosecutors have said he also abused two of the children he had with his daughter. He was convicted in December and sentenced to 30 years in prison on sex abuse charges and of depriving his daughter of her freedom through "private incarceration"
Zaiban said by telephone the rebellion began after guards thwarted an escape attempt by several prisoners. She did not know the number of inmates who tried to flee.
"They then raided the cell where inmates charged with rape and pedophilia were being held and killed six of them, four of whom were decapitated," Zaiban said. The other two, she added, were stabbed to death with makeshift knives.
She said the aborted escape attempt was motivated by the overcrowded conditions: close to 100 inmates were packed into facilities built to hold 30. Overcrowding is common in Brazilian prisons.
The rebellion began Monday and ended Tuesday.
Zaiban said the inmates agreed to return to their cells after authorities said they would consider some of their demands and transfer 14 prisoners to jails nearer to their homes.
The demands included two pounds(one kilogram) of marijuana, a television set, fans to cool the cells and the right to receive home cooked meals, she said.
Asked which demands might be met, Zaiban said, "Marijuana won't be one of them."
(This version CORRECTS that Pereira was convicted, not merely charged.)