Trimet said it would continue production at Voerde and retain the plant's 280 personnel. Financial terms of the deal were not disclosed.
Voerde, which produces 115,000 tonnes of aluminium annually, went insolvent in 2012, blaming high German electricity prices.
The German government's recent decision to continue to give financial relief for high energy prices to power-intensive industries had been a key enabling the takeover, said Trimet owner and supervisory board chairman Heinz-Peter Schlueter.
Trimet expected continued strong aluminium demand in Europe, Schlueter added.
"With the Voerde location we will be able to serve the rising demand," he said.
Trimet produces 640,000 tonnes of primary and cast aluminium and aluminium products annually.
Voerde creditors had voted to continue production at the plant until the end of 2014 while a search for a buyer continued.