Birnbaum managed Charlie Crist’s 1998 unsuccessful campaign against incumbent Senator Bob Graham in Florida.

[12] Previous international political clients include Hungary's Viktor Orbán, Indonesia's Joko Widodo, France's Marine Le Pen, Bulgaria's Sergei Stanishev, Sri Lanka's Maithripala Sirisena, and Ghana's John Mahama.

In 2015, US presidential candidate Ben Carson asked Birnbaum to serve as his chief policy advisor for Israel and the Middle East during the 2016 primaries.

[17] In the 2020 Kyiv local election Birnbaum worked for incumbent Mayor Vitali Klitschko and helped Klitscho win an unprecedented first round re-election with polling data, strategic communications and online ads .

[24] In it, Grassegger draws on an interview with Birnbaum in which he describes how Soros was turned into a pariah in Hungary and a number of other countries due to efforts conceived by Arthur Finkelstein and himself.

[28] Although nothing tangible against the organisation was found, this helped to cement the impression in Hungary that Soros was controlling NGOs and meddling in domestic Hungarian affairs.

In 2018, both the foundation and the Soros-funded Central European University decided that they would leave Hungary and move their offices to Berlin and Vienna respectively.