Nielsen was nominated for the position by President Trump's in October.
Nielsen was Kelly's chief of staff when he headed the department and followed him to the White House, where she served as his principal deputy chief of staff.
Homeland Security oversees the nation's borders, cybersecurity and response to natural disasters, among other areas. Nielsen was the second woman to head this ministry after Janet Napolitano, who was in office from 2009 to 2013.
"I look forward to working closely with Kirstjen and the Department to combat the most critical homeland security challenges facing the United States, including securing our borders, defending against cyber threats, enforcing immigration laws, counterterrorism and more". She served in the Transportation Security Administration during the George W. Bush administration and has also worked as a private-sector cybersecurity consultant. No Republicans opposed her nomination. Sen. Tom Carper, D-Del., asked during her confirmation hearing, according to The Hill.
Several Democrats expressed concerns over Nielsen's close relationship with the White House and potential political interference from the administration.
"Congratulations to Kirstjen Nielsen on becoming the sixth Secretary of Homeland Security", acting secretary Elaine Duke said in a statement Tuesday.
And in a statement released after the Senate confirmed Nielsen, Sen.
"The president has stated as have predecessors at DHS certainly something that I share: There is no need for a wall from sea to shining sea", Nielsen told the senators. She also criticized her reluctance during confirmation hearings to accept human behavior as a cause of global climate change and said Nielsen has "equivocated on protecting 'dreamers, ' " those brought to the country illegally as children and shielded from deportation under Obama.
Nielsen "is ready to answer this call to duty", Johnson said.
It is central to executing specific Trump agenda points, including his hardline approach to immigration, establishing a wall along the US-Mexico border and implementing his travel ban, which the Supreme Court decided on Monday to resume.
While campaigning for the presidency, candidate Trump promised that he would "immediately terminate" DACA after being elected. Ultimately, however, it is the president and Congress who must define what our national immigration policy must be.