As of December 2024, Forbes estimated his net worth at US$21.6 billion,[1] ranked at number 89 on Bloomberg Billionaires Index.

These include: With his mother, Quandt owned 18.3% of Gemplus International, a large digital security company, before its merger to form Gemalto in 2006.

With a second holding company, Aqton SE, Quandt manages other investments, including in renewable energies:[10] Through the non-profit Aqtivator, Quandt supports projects for children, youth, and families with a focus on education, integration, and equal opportunity.

[12][13] Following the 2013 elections, Quandt – together with his mother and his sister – made donations to the Christian Democratic Union (CDU) totaling 690,000 euros.

[21][22] Ahead of the 2017 elections, he gave 50,000 euros each to both the CDU and liberal Free Democratic Party (FDP).

[27] The independent 1,200-page study researched and compiled by Bonn historian, Joachim Scholtyseck, that was released in 2011 concluded: "The Quandts were linked inseparably with the crimes of the Nazis".