The couple, from Russia’s Far Western Kaliningrad exclave, was found guilty of spying for Latvia in late December 2020.
The couple were charged with treason after state prosecutors accused them of sharing a photograph with Latvia of a counterintelligence officer from the FSB who had attended their wedding.
Investigators later additionally charged them with passing classified information to a foreign country.
Zimina was sentenced to 13 years, while Antonets was handed a 12 1/2-year prison sentence. The couple has denied any wrongdoing ever since they were first arrested in July 2018.
Their trial was held behind closed doors in May 2020.
In recent years, the number of cases of alleged high treason has increased dramatically in Russia.
One of the latest high-profile high treason cases involves Ivan Safronov, a journalist and an aide to the Roskosmos space agency chief Dmitry Rogozin.
Safronov was arrested on July 7 and later charged with passing classified materials to the Czech Republic.