Hayden Davies, a former British soldier who was born in Southampton, was labelled a mercenary by Russia.
The court – in the Ukrainian city of Donetsk, currently occupied by Moscow – alleged that Mr Davies was captured in winter 2024 carrying an American-made assault rifle and ammunition.
In a statement, Russian prosecutors said Mr Davies fought for Ukraine’s International Defense Legion after arriving in the city of Ternopil in western Ukraine in August 2024.
A video circulated on encrypted messaging service Telegram on January 1 showing a man identifying himself as Mr Davies, saying he was born in Southampton.
It is not clear what conditions this video was filmed in, with it having been recorded after he was detained.
The video jump cuts throughout as the man recalls his experience in the British Army and then speaks negatively about his decision to fight for Ukraine.
Court footage released by Russian prosecutors shows a man with a British accent speaking through a translator while seated inside a barred cage.
The man identified himself as a member of Ukraine’s foreign legion, saying he had travelled to the country by bus via Poland.
Hayden William Davies (Image: Other)
He claimed he was paid $400 (£300) or $500 per month for his service.
When asked whether he admitted guilt to the charge, he responded “yeah” and nodded.
It remains unclear whether his statement was made voluntarily or under duress.
In a statement to the BBC, the UK Foreign, Commonwealth & Development Office (FCDO) said that Mr Davies had been sentenced “on false charges”, that he was a prisoner of war and that it strongly condemned the sentencing.
It said: “We remain in close contact with Mr Davies’ family and are providing consular support.”
The FCDO said prisoners of war cannot be prosecuted for participating in hostilities under international law.
It added: “We demand that Russia respect these obligations, including those under the Geneva Conventions, and stop using prisoners of war for political and propaganda purposes.”