Thomas started as art director at DDB. In 1972, he was founding partner of Hildmann, Simon, Rempen & Schmitz/SMS, where he became chairman in 1985. 1989 was the year he was elected ?Advertising Man of the Year" in Germany. In 1994, he started Rempen & Partner Werbeagentur. He is a member of the Design Council of Siemens AG, Chairman of Design Centre of Nordrhein-Westfalen and took part in architectural projects along with E. Sottsass, Zaha Hadid, Rem Koolhaas, Jean Nouvel and last but not least Frank O. Gehry who was responsible for the new Zollhof project in Düsseldorf where the agency is now residing.
His client expertise ranges from BAT to Bosch, Bulthaup, Daimler-Benz/Mercedes-Benz, Deutsche Aerospace, Deutsche Post, Dresdner Bank, Erco, Gerling, Gruner & Jahr, Holsten, Merck, Microsoft, Nikon, Osram, Rewe, Ritter Sport, Siemens, Toshiba, TUI, Veltins and Wella.