The transaction is valued at about €900m, including the assumption of nearly €400m of shareholder loans by KET.
E.ON Deutschland chief executive Ingo Luge said the company has reached a successful conclusion regarding the latest transaction.
"The talks with our municipal co-shareholders took place in a constructive atmosphere marked by mutual respect," Luge added.
"E.ON Thüringer Energie is a well-positioned company firmly rooted in the region that we are now passing on to responsible new owners."
Subject to approval by the Thuringian state government, the transaction is expected to be finalized in the coming weeks.
It is also likely that the company would sell its remaining 10% interest in E.ON Thüringer Energie in the near future as a move to sell to reorganize its German regional supply business.
E.ON Thüringer Energie supplies electricity, natural gas and district heat to residential, commercial and industrial customers in Thuringia and parts of Saxony and Saxony-Anhalt.
