The jury concluded Snelson killed 19-year-old college student Jennifer Cusworth after a house party in Kelowna 18 years ago.
Her body was found in a ditch on a rural road in Kelowna.
Years later enhanced testing found Snelson's DNA at the crime scene. The defendant admitted he’d had sex with a woman at the party but did not know who it was, and denied killing anyone.
Snelson, 44, a father of four, was charged with first-degree murder.
His lawyer, Grant Gray, said the manslaughter conviction was unexpected.
"Everybody thought it was either going to be first-degree murder or second-degree murder, or alternatively an acquittal," Gray said later outside the court. "There was nothing wrong with the verdict, it was just a little unanticipated."
The jury took nearly three days to reach its decision.
A sentencing hearing will be held at a later date. A manslaughter conviction can result in anything from a suspended sentence to life in prison.