Before the act, it was only possible to proscribe organisations connected to terrorism in Northern Ireland.
Wagner will now join other organisations like the Hamas and Boko Haram that have been proscribed by the UK, the BBC reported.
In a statement, Home Secretary Suella Braverman said Wagner was “violent and destructive… a military tool of Vladimir Putin’s Russia”.
She said its work in Ukraine and Africa was a “threat to global security”.
“Wagner’s continuing destabilising activities only continue to serve the Kremlin’s political goals. They are terrorists, plain and simple – and this proscription order makes that clear in UK law,” Braverman added.
Wagner had played a key role in Russia’s invasion of Ukraine, as well as operating in Syria and countries in Africa including Libya and Mali.
Its fighters have been accused of a number crimes including killing and torturing Ukrainian citizens.
The UK Foreign Office had earlier imposed sanctions on the group, including freezing the assets of Wagner late chief Yevgeny Prigozhin and several top commanders.
Prigozhin, who led a failed mutiny against the Russian military leadership in June, was killed in a plane crash along with other Wagner members on August 23.
