Nielsen was Kelly's chief of staff when he was DHS Secretary, and Kelly later brought her into the same role at the White House, where some staffers came to see her as the former general's dreaded enforcer.
Kirstjen Nielsen, Chief of Staff of U.S. Department of Homeland Security, center, walks to Air Force One as she departs Tuesday, Aug. 22, 2017, at Andrews Air Force Base, Md. She now serves as Kelly's principal deputy chief of staff and was also his chief of staff at the Department of Homeland Security.
"I share the president's profound commitment to the security of our country and the safety of the American people", Nielsen said during the ceremony.
Federal court reinstates Ezekiel Elliott's 6 game suspension
If it imposed immediately, he would be eligible to return for Dallas's November 30 game against the rival Redskins. Authorities in Columbus, Ohio, did not charge Elliott with a crime.
Her nomination must now be confirmed by a vote in the Senate. She is the first nominee for the homeland security post who had served in the department, according to the statement.
She has a reputation as an expert on cybersecurity matters, and if confirmed, she would be the first former DHS employee to run the department.
Elaine Duke has been serving as acting DHS secretary since Kelly departed the agency for the White House in July. That might have contributed to Trump thinking about her highly.
"I am pleased that the President has finally made a nomination for Secretary of Homeland Security after letting the critical national security position remain vacant as the nation faced multiple major hurricanes and a domestic terrorism attack".