[2] During the Obama administration, Miller headed the Office of Public Affairs at the Department of Justice,[3] and served as the spokesman for U.S. Attorney General Eric Holder.

[5] During the early days of the Biden administration, he led the efforts to get Antony Blinken's nomination as U.S. Secretary of State confirmed.

[7] As spokesperson for the State Department, Miller has repeatedly been accused or rebuked by journalists for laughing about inappropriate topics while communicating the U.S. government's public policy positions during the Israel–Hamas war.

[8] While answering questions pertaining to the Gaza death toll, Miller was accused by a man, understood to be journalist Sam Husseini, of "smirking".

[9] Several months after the "smirking" incident, Miller was rebuked by Matt Lee of the Associated Press, for laughing while answering a question about U.S. provided aid not reaching Gaza.

During the farewell address, journalist Shaun Tandon of Agence France-Presse made mention of how Miller had "received lots of criticism for some of your responses".

[18] The following day, Miller attended Secretary of State Blinken's farewell address and facilitated the question and answer segment.