The recipient of numerous grants, awards, and national recognitions, she was president of the Society for Historians of the Early American Republic from 2009 to 2010.
Zagarri received her Ph.D. from Yale University where she was the last doctoral student of the eminent early American historian, Edmund S. Morgan.
She is the author of The Politics of Size: Representation in the United States, 1776-1850 (Cornell University Press, 1987), A Woman’s Dilemma: Mercy Otis Warren and the American Revolution (Harlan Davidson, 1995; 2nd.
She has appeared as an on-camera historian on CSPAN’s Book TV, CSPAN's "Morning Journal," PBS’s “George Washington: The Man who Wouldn’t Be King,” and the Fairfax Television Network’s “The Real Martha Washington.” In 2009 she was elected President of the Society for Historians of the Early American Republic (SHEAR).
In 2011, she received the Scholarship Award from GMU's College of Humanities and Social Sciences and was appointed a Distinguished Lecturer by the Organization of American Historians.