William McDermott, 41, who left his job as executive vice-president of worldwide sales at Siebel earlier this month, will replace SAP's US interim chief executive officer, Leo Apotheker.
McDermott will be the enterprise software company's fourth US chief executive officer in three years, including Apotheker. He will start work next week, reporting directly to Apotheker, president of global field operations. He will be responsible for all SAP's business activities in the US and Canada.
Siebel and SAP are fierce rivals in the market for enterprise resource planning (ERP) software, and in the late 1990s, Siebel hired more than 20 employees away from SAP America, including the division's former president, Jeremy Coote.
One of the immediate challenges facing McDermott, who was CEO of Gartner before joining Siebel, will be to boost SAP's US software licence sales, which plummeted more than 30% in the second quarter.