Werth has competed in the Olympics four times in 1992, 1996, 2000 and 2008. In those four games she won eight medals, five of them gold. Werth has also won seven Dressage World Championship medals, six of them gold. She has competed multiple times at the European Dressage Championships, earning several gold and silver medals. At the 2008 Olympics she won the team championship together with her colleagues Heike Kemmer and Nadine Capellmann. Isabell Werth worked alongside Bates Australia to develop the Isebell Dressage Saddle available in Bates and Wintec.
Werth rode Gigolo, owned by Uwe Schulten-Baumer, her coach from 1986 until 2001. On Gigolo, she won all her championships between 1992 and 2000, save for the 1999 European Championships in Arnheim, where she rode Anthony FRH. She currently rides two horses on the highest level: Warum Nicht FRH and El Santo NRW. She competed at the Olympic Games with Satchmo. Satchmo retired in November 2011.