The €13bn award stems from an arbitration hearing earlier this month, during which Gazprom was accused of breaching gas supply contracts.
European gas prices rose by 2.6pc following the decision, as energy traders signalled fears of disruption to Russian deliveries of gas elsewhere in Europe.
In a statement on Wednesday, Uniper said: “Uniper decided today to terminate its long-term Russian gas supply contracts and thus legally ended the long-term gas supply relationship with the Russian state-owned company Gazprom Export.
“The decision was made possible after an arbitration tribunal awarded Uniper the right to terminate the contracts and awarded it an amount of more than €13bn in damages for the gas volumes not supplied by Gazprom Export since mid-2022.”
Since both companies are owned by their respective governments, some have seen the legal battle as more than a traditional corporate dispute.
However, there are doubts as to whether Putin will ever allow Gazprom to pay the money owed to Uniper – especially as it would be passed to the German federal government.
Michael Lewis, the Briton last year appointed as Uniper’s chief executive, said: “This ruling provides legal clarity for Uniper.
“With the right of termination that we received in the arbitration ruling, we are ending the contracts with Gazprom Export. Uniper’s legal position was also confirmed on the issue of damages. Any amounts would flow to the German federal government.
“From today’s perspective, it is not yet clear whether significant amounts are to be expected.”
Uniper operates roughly 22.5 gigawatts of generation capacity across Germany, Holland, Sweden and Hungary, making it one of the world’s largest power producers.
Well over half its generation comes from gas and coal, although Uniper has pledged to become carbon neutral by 2040.
Its assets include Ratcliffe-on-Soar, Britain’s last coal-fired power station, sited just south of Nottingham.
The station is expected to close in September, finally ending the UK’s reliance on burning coal – the dirtiest of fossil fuels – to generate electricity.