A jury deliberated for 4 hours before finding Kevin Liverpool, 35, and Junior Bradshaw, 32, both of Manchester guilty of planning to grab the 25-year-old singer at her Devon County home and decapitate her, The Guardian reported.
Judge Francis Gilbert sentenced Liverpool to life in prison and he must serve at least 10 years and eight months before he becomes eligible for parole. Bradshaw is to be sentenced at a later date, the newspaper said.
"You intended to rob her and kill her and dump her body in the river, according to your words, and then leave the country with your accomplice Junior Bradshaw," the judge said.
Authorities said the pair were armed with a samurai sword, hammers, a metal spike and knife as they set out on their criminal mission on June 11. They also had balaclavas, gloves, body bags, gaffer tape, a roll of plastic bags and maps showing the area where the singer lived.
They botched up their scheme trying to get to her house. First, they smashed their car after driving off without paying for gas at a service station in Gloucestershire. While the police who showed up at the accident scene didn't uncover their true intent, the pair later got lost and asked a postman for directions.
Area residents called police after seeing them "agitated and behaving abnormally." This time, police found the incriminating evidence and arrested them.
Stone, best known for her song "Fell in Love With a Boy," said she was relieved by the outcome of the case, The Daily Telegraph reported.
"I'd like to thank everyone for all their support and kind wishes," she said in a statement.
"I am relieved the trial is now over and that these men are no longer in a position to cause harm to anyone."