If confirmed by the Senate, Kirstjen Nielsen will oversee 240,000 employees at the Department of Homeland Security. DHS is responsible for immigration, border control and cyber-security, among other areas.
Kirstjen Nielsen faces a Senate confirmation process starting on Wednesday when she goes before the Senate Homeland Security Committee.
President Donald Trump nominated the 45-year-old to lead the Department of Homeland Security (DHS) last month after he earlier had brought John Kelly from DHS secretary post to the White House to be his chief of staff.
Nielsen was Kelly's top deputy at the DHS and moved with him to the White House, where she helped the retired general reorder a chaotic executive branch that marked the first months of the Trump administration.
If confirmed by the Senate, she will take over a massive department with 240,000 employees.
DHS was established after the 9/11 terror attacks to address security failures and lack of coordination across agencies.
It is also responsible for managing disaster responses and cyber-security, among other issues.
Nielsen served in President George W. Bush's administration as a special assistant and member of the Homeland Security Council.
She also started up the Offices of Legislative Policy and Government Affairs at the TSA, meaning she brings with her previous experience of the inner-workings of DHS.
After leaving the Bush administration, Nielsen worked in the private sector as counsel and a president of the Civitas Group consulting firm. She then established Sunesis Consulting, providing consulting services to domestic and international clients on cyber-security and preparedness issues.
cw/rc (AP, Reuters)