He is a senior fellow in governance studies at the Brookings Institution, a CNN legal analyst, and the co-founder of the States United Democracy Center.

From 1985 to 1988, between college and law school, Eisen worked as the assistant director of the Los Angeles office of the Anti-Defamation League.

[15] He earned the nickname "Dr. No" for his stringent ethics and anti-corruption efforts and became known for limiting registered lobbyists from taking positions in the administration.

[10] During 2009 and 2010, Eisen also contributed to the administration's open government effort, including putting the White House visitor logs on the internet; its response to the campaign finance decision in Citizens United v. FEC; and its financial regulatory plan, which is the basis for Dodd–Frank.

[18] As ambassador, he developed a "three pillars" approach to the U.S.–Czech relationship, emphasizing (1) strategic and defense cooperation; (2) commercial and economic ties; and (3) shared values.

[22] He also supported the Middle East peace process, including posting the first investment conference on the "Kerry Plan" in Prague together with former British Prime Minister Tony Blair and former secretary of state Madeleine Albright.

[27] Eisen's nomination received bipartisan support, including from Republican senators and conservative foreign policy scholars.

[2] At Brookings he has contributed to reports on open government,[31][32] the emoluments clause,[33] presidential obstruction of justice,[34] and anti-corruption efforts in the natural resource sector.

[35] A prolific writer, he often contributes op-ed pieces to The New York Times,[36][37] The Washington Post,[38] Politico,[39] USA Today,[40] and other national publications.

[42] He has also authored "Democracy's Defenders: U.S. Embassy Prague, the Fall of Communism in Czechoslovakia, and Its Aftermath" and "A Case for the American People: The United States v. Donald J.

He served as co-counsel on an amicus brief filed in opposition to Lindsey Graham's motion to quash a subpoena in the Fulton County Special Grand Jury investigation of attempts to overturn the 2020 election results in Georgia.

[51] Eisen has co-written reports for States United including a guide to the Electoral College vote count and the January 6, 2021, meeting of Congress.

[54] Director Wes Anderson has credited Ambassador Eisen as an inspiration for the character of Deputy Kovacs in his 2014 film The Grand Budapest Hotel.

[56] Anderson again referred to Eisen in the closing scene of Isle of Dogs, captioning a character as ethics czar in the new government of Megasaki.