There was "no doubt" that Laurent Ségalat, 48, killed his 67-year-old step-mother Catherine Ségalat at her home in the Swiss town of Vaux-sur-Morges on January 9th 2010, the Lausanne court ruled.
The ruling reversed a lower-court verdict in June, which acquitted Ségelat precisely on the grounds that there was "sufficient doubt" about his guilt.
The prosecution had failed to come up with a motive for the crime or produce a murder weapon.
Ségalat himself, who attended the one-day appeal court hearing a day earlier, did not show up for the verdict and sentencing Friday.
His lawyers said they had not been in touch with him since Thursday evening.
The prosecutor in the case said he would request Ségelat's immediate arrest, insisting he was a flight risk.
Ségelat, a researcher in genetics at the prestigious French CNRS centre, who lives on the French side of Lake Geneva, was found at the scene of the crime with scratch marks on his face and arms.
There is "no doubt, the defendant is the perpetrator of the serious wounds inflicted on the victim," the three Lausanne judges said in Friday's ruling.
They stressed that "most of his explanations for the scratches show that he is not telling the truth."
They noted too that Ségelat had waited three hours from the time he said he had discovered his step-mother's body before calling for help.
Investigators had found his DNA under her nails, they noted; and he had twice changed out of blood-soaked shirts, the court said.
The judges ruled that Ségelat's use of bleach to clean up before calling for help had been designed to cover his tracks, the judges ruled.
Ségelat was also ordered to pay 30,000 francs ($32,000) to each of the victim's two sisters, who were the civil plaintiffs in the case.