Theiler attended SBS Swiss Business School in Zurich but left to focus on his professional show jumping career.

Other areas of expertise; include structural civil engineering and real estate management services.

[14][15] Theiler founded CSI in 1988 with his brother Urs, together the pair used their own startup capital of roughly CHF 2 million to launch their first event, which attracted 21,000 spectators on its debut.

According to Bilanz, today CSI is the largest and most lucrative indoor equestrian tournament in the world,[16] with over one million spectators worldwide.

[26] These riders include, Beat Mändli who rode Theiler's horse Idéo du Thot finished 3rd in the 2006 FEI Show Jumping World Cup which took place in Kuala Lumpur.

[32] They have additional homes in Knysna on the Western Cape Province,[33] Gandria on Lake Lugano and Klosters where they own Chalet Eugenia.