Gabriel Armandou, 79, was given a five-year suspended sentence for the attack on his wife Paulette in September 2008 at their home in Fresnes, south of Paris.
"I am happy, I want to cry," Armandou told journalists as he left the court.
Armandou had not claimed it was a mercy killing but said he had "cracked" under the pressure of caring for his wife, who had been suffering from Alzheimer's for eight years and whose condition deteriorated in the three months before the murder.
Paulette Armandou was found nearly naked in the couple's living room with multiple injuries and bruises. Her face was swollen and a blood-stained floor mop was found nearby.
A post-mortem report said she had been hit on the head, neck, chest and back.