Nielsen has a background in homeland security policy and strategy, cybersecurity, critical infrastructure and emergency management, according to the White House. She previously served in the administration of President George W. Bush.
Nielsen formerly served as John Kelly's chief of staff when he held the position of Trump's first DHS secretary. She moved with Kelly to the White House when Trump tapped him to serve as his own chief of staff, and was quickly named principal deputy.
"(Nielsen) plays a crucial role in managing White House functions and coordinating with federal agencies," Trump said on Thursday. "She has won the universal respect of my entire cabinet and staff."
Elaine Duke has been filling in as acting secretary of the department since Kelly's departure, leading the department through a series of back-to-back hurricanes, including one that devastated most of Puerto Rico. But she raised eyebrows when she described that storm's aftermath as a "good news story."
Nielsen's nomination will have to be approved by the Senate. Trump on Thursday urged senators to quickly confirm the nomination.
"In light of the serious threats facing our country and the urgent disaster recovery efforts, I call upon the Senate to put politics aside and confirm this tremendously qualified and talented nominee with a strong bipartisan vote," Trump said. "Kirstjen has my full faith and confidence, and she also has the complete confidence of the law enforcement officers, dedicated professionals and senior leadership at the Department of Homeland Security."
The Associated Press contributed to this report.