The court in Meilen, near Zurich, also found the man guilty of raping a former girlfriend two months before the murder, as well as a range of cases of sexual assault, the ATS news agency reported on Wednesday.
The court did not give the 32-year-old perpetrator's name, but British media have identified him as Bennet V, the son of a wealthy aristocratic Zurich art gallery owner, who also ran his own contemporary art gallery in the city.
He also holds British and German citizenship, according to Blick.
On December 30th 2014, his victim, identified by media as 23-year-old British national Alex M., had been visiting his friend's family villa in the swanky Kuesnacht municipality, on the "gold coast" of Lake Zurich.
The art dealer's parents were away, holidaying in the Engadine Alpine resort, where many rich and famous from around the world like to ring in the New Year.
The Swiss and his British victim, who graduated from the prestigious Scottish boarding school Gordonstoun -- once attended by Prince Charles -- had spent the night out on the town in Zurich, returning to the villa at around 4am.
Once back, the two had gotten into a fight, which ended with the Swiss strangling and beating his friend to death with a massive candlestick holder.
The art dealer, who has admitted the murder, insisted through his lawyers he had been hallucinating after taking a cocktail of drugs and alcohol, and had thought his friend was an alien trying to kill him.
The judges however did not lend credence to his explanation, describing the murder as "cruel and violent," according to ATS.
The judges did meanwhile take into consideration that he had acted under the influence of drugs, handing him a lesser sentence than the 16 years requested by the prosecution.