Valery Permyakov, a soldier at a Russian base in the Armenian town of Gyumri, pleaded guilty to killing seven members of a family, RIA Novosti reported on Friday.
The family, including a six-month-old baby, was killed as a result of an armed assault on January 12, 2015.
Permyakov was arrested and later charged with the murder of two or more persons under the Armenian Criminal Code.
On August 12, Permyakov was found guilty of desertion, theft of weapons and sentenced to 10 years in prison.
The murder case was singled out for considering it in a separate procedure and passed to the Armenian authorities.
On October 13, Permyakov was found sane. According to experts, he was not in the heat of passion while committing the crime. He also could recognize the consequences of his actions.
On October 16, Permyakov was additionally charged with armed assault, home-invasion robbery and attempted border crossing.