He previously served as the Assistant Attorney General of the Antitrust Division of the U.S. Department of Justice from 1996 to 2000 during the administration of President Bill Clinton.

The MHLP was an independent non-profit organization that brought class-action suits to establish rights for mentally and developmentally disabled clients.

In the 1990s, Klein served in the White House Counsel's office under President Bill Clinton, before being appointed to the United States Department of Justice.

Prior to his appointment to chancellor in 2002[7] by Mayor Michael Bloomberg, Klein was counsel to Bertelsmann, an international media group.

[8] Ultimately, the position went to the chief executive officer of Chicago Public Schools, Arne Duncan, then to New York State Education Commissioner John King Jr.

[9] Klein has been criticized for not seeking to alter this arrangement or to curb the conduct of the Police Department's school safety agents in the face of allegations of abuse.

[11] Despite their opposing positions in the Justice Department antitrust case against Microsoft, Klein was able to work with the Gates Foundation to fund the creation of smaller schools in New York City.

"[20] The program's creator Mark Willner stated that (Khalidi) "spoke on geography and demography," and that "There was nothing controversial, nothing political.

Finally, in 2014, the Education Department decided to abandon the system, due to its high cost, limited functionality, and little use by parents and staff.

No curricula existed at the time for this approach, leading Lucy Calkins to write a textbook on the subject in three weeks ahead of the 2003–2004 school year.

[26] On November 9, 2010, Bloomberg announced that Klein would resign as chancellor and would take a position as an executive vice president for News Corporation.

In February 2011, NYCDoE Communications Director Natalie Ravitz announced that she would be joining News Corp as Klein's chief of staff.

He also acquired Wireless Generation, the technology company that developed and managed ARIS, the city's school data warehouse.