Financial terms of the transaction were not disclosed.

WestLB Mellon Asset Management was formed in early 2006 as a 50/50 joint venture between BNY Mellon and Portigon. The company has over 170 employees and over €25 billion (about $32.3 billion) in assets under management.

The deal comes at a time when M&A activity in the wealth and investment management sector has been relatively steady. In the summer, Bank of America Merrill Lynch sold its non-US wealth management business to Switzerland's Julius Baer.  The first two quarters of the year saw 57 merger and acquisition deals in the asset management sector, with deal volume holding exactly steady compared to the first half of 2011, according to Freeman & Co. (That report was carried out prior to completion of the Julius Baer/Merrill transaction.)  Among other deals recently, Founders Financial Network and Buckingham Asset Management - both Focus Financial partner firms - entered into an agreement in which the former will merge into the latter, creating a $17 billion RIA powerhouse in St Louis, MO.

Werner Taiber, who has most recently served on the managing board of Portigon, will serve as chief executive, pending approval by German regulators. Taiber will report to Harris and Curtis Arledge, CEO of BNY Mellon Investment Management.

"The completion of this transaction is an important milestone for us," Mitchell Harris, president of BNY Mellon IM said in a statement. "Germany has one of the most sophisticated investment industries globally, and is a key strategic priority for BNY Mellon."

BNY Mellon Investment Management has $1.3 trillion in AuM.