Mr Miller’s tweet came after his boss left the White House and Mr Biden was sworn in as the 46th president of the United States.
Once in the Oval Office Mr Biden immediately reversed Mr Trump’s ban on immigration from several Muslim-majority countries and cancelled funding for the southern border wall.
“Today, [Biden] pledged to be a president for all Americans,” tweeted Mr Miller.
“It’s unclear how all Americans are served by opening travel from terror hot spots, proposing a giant amnesty, or halting the installation of security barriers along the Southwest border.”
Mr Biden wants to implement an immigration plan that would give 11 million undocumented people a path to citizenship.
Mr Miller was responsible for many of the Trump administration’s hardline immigration policies, including the family separation policy.
Twitter users were quick to slam Mr Miller over the policies he had helped bring in over the last four years.
“You helped incite a terror attack on Congress and ordered the stealing of babies from their parents,” tweeted political analyst Mehdi Hasan.
“National security cannot be a facade for racism. He’s not the first but he needs to be the last,” said former CIA analyst Nada Bakos.
