"Ferdinand Piech will sell most of his shares to other members of the Porsche-Piech family" which controls VW parent company Porsche SE (PSE), a spokesman for the holding company told AFP.
The 79-year-old holds a sizeable stake -- worth around 15 percent or 1 billion euros ($1.1 billion), according to German media reports -- in PSE, alongside other members of the dynasty descended from the inventor of the VW Beetle.
PSE, a purely financial firm with no direct link to sports car maker and VW subsidiary Porsche, in turn controls the Volkswagen group with 52 percent of its voting rights.
The spokesman refused to say exactly how much of his stake Piech will sell or to which other family members.
Monday's sale is still subject to approval from financial regulators and competition authorities in several countries, the holding firm clarified in a statement.
One foundation controlled by Piech, which "indirectly holds a limited stake," will not give up its stock, PSE said.
The former chairman will also remain a member of PSE's supervisory board "until the transaction is finalised," the firm said, declining to specify an exact date.
Piech has been at odds with other family members for weeks over the so-called 'dieselgate' scandal which has shaken the firm since September 2015.
German media reported that he had told prosecutors VW bosses knew about emissions cheating earlier than they admitted.
After fitting 11 million cars with devices allowing them to fool emission tests, Volkswagen has so far set aside more than 22 billion euros to cover fines and compensation -- but experts estimate the final bill could be much higher.
Piech led VW from 1993 to 2002, before becoming head of the supervisory board until 2015.
His mother Louise was the daughter of Porsche founder and Beetle inventor Ferdinand Porsche, while his father ran the historic factory belonging to Volkswagen in Wolfsburg, north Germany, during the Second World War.