EON directors "approved the acquisition of a substantial package comprising power stations and other shareholdings above all in Spain, France and Italy," a statement said.
The German group is to pay €8.9 billion directly and take on debt currently estimated at around €2.9 billion.
It saw the "extensive transaction as a constructive way of ending the dispute over the acquisition of a majority interes in the Spanish energy company Endesa."
The Italian power group Enel and Spanish firm Acciona were also involved in the deal.
EON dropped its bid for Endesa in April 2007 following a battle of more than one year against Spanish government opposition, in exchange for an agreement that allowed the German firm to buy major assets in return.
The EON statement quoted chief executive Wulf Bernotat as saying: "With this transaction we are considerably expanding our position in Spain, where we are already strong in the wind power market, and Italy."
He added that "EON now has an international presence unmatched by any other energy company, thus obtaining an even better platform for further profitable growth in Europe."
In Madrid, Endesa said Friday in a statement that it would make a pre-tax capital gain of €4.5 billion on the transaction.