Brown's departure follows the launch of Adwen, the joint-venture between Gamesa and Areva. He has been replaced by Adwen general manager Luis Alvarez, who previously headed up Gamesa's offshore activities.
Additionally, asset manager Greensolver said it has appointed Brown as a board director. The company said the move was part of a drive to develop its presence in the UK offshore and onshore wind markets.
Prior to joining Areva in 2011, Brown headed up his own "leadership consultancy", Excellence in Leadership. Before that he spent four years with NEG Micon as managing director.
Brown was also made RenewableUK chairman in 2014.
In a statement, Areva confirmed Brown had left the company. It said: "Julian Brown has decided to pursue personal projects outside Adwen.
"Adwen implements a global organisation across Europe, led by Luis Alvarez, Adwen's general manager. Luis Alavarez is also heading the UK offices."