Rein has been active in the financial world since 1980. He started as a Foreign Exchange administration employee at Albert de Bary Bankiers & Co. In 1985 Rein switched to Schamhart Independent Floorbrokers. This was the largest independent order execution company on the Options Exchange. From 1995 to 2004, Rein worked as a securities trader and advisor at SNS Securities and then worked successively at AFS Capital Management, Indexus Group and Boer & Olij Securities. Rein is DSI registered as a Sr Investment Advisor and has been affiliated with Noesis B.V. since March 2020.