Siebel was an executive at
Oracle Corporation between 1984 and 1990, holding several management positions. He was the CEO of Gain Technology, a multimedia software company that merged with
Sybase in December 1992. He is the chairman of First Virtual Group, a
diversified holding company. In 1993, Siebel left Oracle and founded
Siebel Systems. By 1999, Siebel Systems was recognized by
Deloitte & Touche as one of the most rapidly expanding technology companies in the United States. In 2000, Siebel reported that Siebel Systems had grown to over 8,000 employees in 32 countries, with more than 4,500 corporate customers and annual revenue exceeding $2 billion. Siebel Systems was acquired by Oracle in 2005.
C3 AI Siebel founded enterprise artificial intelligence company
C3 AI in 2009 and has led the company as CEO since 2011. He transitioned to the role of executive chairman in 2025 after being diagnosed with an
autoimmune disease that left him visually impaired. ==Honors and awards==