He served as Under Secretary for Science in the United States Department of Energy from 2006 until 2009, when he was replaced by Steven E. Koonin.

[2] Orbach continues to do research as a tenured professor in the Cockrell Family Dean's Chair for Engineering Excellence at the University of Texas.

From 1982 to 1992, he served as the provost of the College of Letters and Science at UCLA, and from 1992 to 2002 as chancellor of the University of California, Riverside.

After June 1, 2006, he was the first Under Secretary for Science, for which President George W. Bush nominated him after the position was created by the Energy Policy Act of 2005.

He resigned November 30, 2012 in response to a report critical of the Energy Institute's handling of potential conflicts of interest involving the geologist Charles G. Groat.