Johanna Bruhn became a secretary in her Future husband's office in the 1950s and eventually became his personal assistant. The two married in 1960. After his death in 1982, she was a major shareholder in BMW and sat on its supervisory board from 1982 until she retired in 1997. Much of that time she served as deputy chairwoman of the board. She owned 16.7% of BMW at the time of her death.
The two children of her marriage, Stefan and Susanne, are also substantial shareholders in BMW and now sit on the supervisory board of the company. Police prevented an attempt to kidnap her and her daughter Susanne Klatten in 1978. Johanna lived quietly in Bad Homburg.
A programme by the German public broadcaster, ARD, in October 2007 described in detail the role of the Quandt family businesses during the Second World War. As a result, four family members announced, on behalf of the entire Quandt family, their intention to fund a research project in which a Historian will examine the family's activities during Hitler’s dictatorship.
As of August 2014, the Quandt family is estimated to be worth $46.3 billion. Johanna Quandt died at the age of 89 in her home in Bad Homburg near Frankfurt am Main.