The incident occurred in June 2012 in the resort town of Loèche-les-Bains in the canton of Valais, where the ex-banker had a holiday apartment, according to the Haut-Valais district court.
His lawyer argued that he killed the girl in an act of negligence while the two were playing alone during a weekend together in the apartment.
But the court rejected the argument, finding the resident of Founex in the canton of Vaud guilty of murder.
Court evidence found that the man, who had lost his job twice over a period of years and suffered from depression, acted out of vengeance after his wife decided to leave him.
The man's lawyer said his client maintained that they were playing “who is the boss”, a game that consisted of strangling each other until one of them said “stop”, Le Temps newspaper said.
In addition to the jail sentence, the former exec was ordered to pay the victim's mother 35,000 francs in damages and to cough up more than 41,000 francs in legal costs.