A White House official described Nielsen as on the "inside track" for the job, adding that the president is "very fond" of her.
President Donald Trump plans to nominate Kirstjen Nielsen, a top aide to White House Chief of Staff John Kelly, to head the Homeland Security Department, an administration official said.
She is now the White House principal deputy chief of staff.
Nielsen is an attorney who has experience in homeland security and cybersecurity, having served on the White House Homeland Security Council under President George W. Bush. "It's a little concerning that she seems to have little background in immigration security and policy, but those individual agencies are in good hands already, and there is a strong core of career managers", said Jessica Vaughan, director of policy studies at the Center for Immigration Studies, which favours more limits on immigration.
Nielsen would be the first former DHS staffer to lead the department, which was created by former President George W. Bush in 2003.
Nielsen's departure from the White House would mark the latest upheaval in Trump's White House team. That comment drew a critical response from San Juan Mayor Carmen Yulin Cruz, who has been an outspoken critic of how the Trump administration has responded to the situation on the ground in Puerto Rico. The department also is responsible for US border security. She also ran the Transportation Security Administration's offices of legislative policy and government affairs, a section she started. She now serves as deputy White House chief of staff.
"Kirstjen can hit the ground running and there won't be a learning curve", Ridge said.