[2] Ellenson was born on June 25, 1947, in Brookline, Massachusetts, and grew up in an Orthodox Jewish family in Newport News, Virginia.

In 2015, Ellenson was appointed a distinguished visiting professor at New York University and he taught there in the Skirball Department of Judaic Studies in 2015–2016.

He has written extensively on the origins and development of Orthodox Judaism in Germany during the nineteenth century, Orthodox legal writings on conversion in Israel, North America, and Europe during the modern era, the relationship between religion and state in Israel, the history of modern Jewish religious movements, and American Jewish life.

Ellenson authored or edited seven books and over 300 articles and reviews in a wide variety of academic and popular journals and newspapers.

President George W. Bush appointed Ellenson to serve on delegation to accompany him to Jerusalem for the celebration of the 60th anniversary of the State of Israel in May 2008.