[citation needed] Thielen was a partner and shareholder of RWP Corporate Finance advisors, which was later acquired by Investec group.

[3] Thielen founded his own family office Gryphion in 2019 in order to manage his assets with a focus on private equity investing.

[2] Thielen has served as a non-executive member of the board of RPS plc, an LSE quoted company active in environmental consultancy; and a non-executive board member of arxes NCC AG, an IT service provider quoted at the Frankfurt Stock Exchange.

[8] VVD politician Hans van Baalen has mentioned Thielen as one of the sponsors of this 2014 campaign for the European Parliament.

[10] Thielen was also a member of the visiting faculty of the Rotterdam School of Management (Erasmus University), where he taught on mergers and acquisitions on the RSM MBA program.