President Barack Obama plans to nominate Jeh Johnson, the Pentagon's former top lawyer, to be the next Homeland Security Secretary, sources tell CNN.

The nomination is expected on Friday. He must be confirmed by the Senate.

Johnson would replace former Secretary Janet Napolitano, who left the Cabinet post earlier this year to head California's public university system, and would be the fourth secretary of the Department that was created in response to the 9/11 attacks.

Johnson was appointed the Defense Department's General Counsel in 2009 after serving on Obama's transition team.

With 10,000 military and civilian attorneys working for him, Johnson was responsible for the prior legal review and approval of every military operation approved by the President and Defense Secretary.

He stepped down earlier this year and reentered private practice.

If confirmed, Johnson would take over the top security job following Obama's public recalibration of the "war on terror," saying May the United States should no longer see it as a "self-defeating" perpetual fight, but one that must at some point end, "like all wars."

The Homeland Security Department is meant to coordinate the U.S. domestic security apparatus, encompassing everything from the FBI to the Border Patrol. It not only keeps an eye on al Qaeda and other terror threats, but also covers border security, immigration enforcement, cybersecurity, transportation security and disaster assistance.

Johnson's nomination comes three months after Napolitano announced she would step down in July. A series of names were floated as potential candidates for the job, including New York City Police Commissioner Ray Kelly and Boston Police Commissioner Ed Davis.