Christopher Halliwell had denied killing the 20-year-old whose body was found in a shallow grave in Gloucestershire.
It took the jury at Bristol Crown Court just three hours to find the 52-year-old guilty of murder.
Halliwell – who represented himself – laughed as the verdict was read out. He had claimed drug dealers had killed her.
Becky Godden’s body was found in 2011, nearly a decade after she disappeared from Swindon.
Halliwell will be sentenced on Friday.
