Siegel is a lifelong resident of the Brooklyn area of New York City. He graduated from Brandeis University, Siegel worked at The New York Sun as an editorial writer and the paper's first OpEd page editor when it launched in 2002. He would go on to found the web magazine New Partisan with Tim Marchman. Siegel was editor-in-chief of New York Press in 2005 and 2006, and now works as an editor at The Politico. He has also immersed himself in politics at times, working as a researcher for political consultant Hank Sheinkopf, and served as policy director for New York State gubernatorial candidate Thomas Suozzi in 2006.

Siegel is co-author (with his father Fred Siegel) of The Prince of the City: Giuliani, New York and the Genius of American Life, which appeared on the 100 Notable Books of 2005 list compiled by The New York Times newsmagazine. Siegel's commentary has appeared in City Journal, The New Republic, The New York Post, The New York Observer and The Weekly Standard. He has made guest appearances on CNN, MSNBC and National Public Radio.