Sixty-eight year old William Holmes, an American living in Alessandria, Piedmont, turned himself in to the police in November 2012, ten days after he killed his wife Patricia Ann Holmes, Andkronos reported.
Holmes claims his wife, who was severely crippled by chronic rheumatoid arthritis, asked him help her die.
Holmes administered her with a huge dosage of the sedative Lexotan, but when it failed to have the desired effect, he stabbed her through the left lung with a kitchen knife.
Euthanasia is illegal in Italy, punishable with jail sentences of up to 15 years.
The strict penalties for assisted suicide have created a huge boom in 'suicide tourism', whereby sick Italians frequently travel to neighbouring Switzerland where they can end their lives without being prosecuted.
Holmes has always maintained his innocence, describing the act as a 'mercy killing' which he carried out 'for selfless ends.' However, In 2013 a Turin court sentenced him to nine years and four months in jail for the murder of his wife.
In a bid to reduce or overturn his sentence, Holmes appeared before Italy's Court of Cassation on Thursday, asking that it consider the extenuating circumstances that caused him to act.
But the court rejected his appeal and upheld the initial sentence.
In its verdict, the court said that his killing had not been entirely selfless, but that he had acted 'with the parallel intention of no longer being obliged to continually assist his terminally ill wife'.