|Born||1955 (age 63–64)|
|Residence||Ossining, New York|
|Relatives||Michael Ellsberg (paternal half-brother)|
Robert is the son of Carol Cummings, the daughter of a Marine Corps Brigadier General, and the American military analyst and whistleblower, Daniel Ellsberg. He is the older brother of epidemiologist Mary Ellsberg and author Michael Ellsberg. In 1975, at age 19, he dropped out of college, intending to spend a few months with the Catholic Worker Movement.
He stayed to become the managing editor of The Catholic Worker for two years (1976–8), a job that would introduce him to Dorothy Day and consequently would allow him to work with Day for the last five years of her life. This life-changing experience prompted him to convert to Catholicism.
In 1987 he began work as editor-in-chief of Orbis Books. He is the author of several books, many of which have received awards; his Blessed Among All Women tied a Catholic Press Association record by winning awards for Gender, Spirituality, and Popular Presentation of the Catholic Faith. He is the editor of the published diaries and letters of Dorothy Day.
- Gandhi on Christianity (1991)
- All Saints: Daily Reflections on Saints, Prophets, and Witnesses for Our Time (Crossroad, 1997)
- The Saints' Guide to Happiness: Practical Lessons in the Life of the Spirit, Doubleday, 2005. ISBN 978-0-385-51566-5
- Blessed Among All Women: Reflections on Women Saints, Prophets, and Witnesses for Our Time (Crossroad, 2006).
- The Duty Of Delight: The Diaries of Dorothy Day. ISBN 0-87462-023-6 (editor) Marquette University Press, Milwaukee, 2008
- All the Way to Heaven: The Selected Letters of Dorothy Day. ISBN 978-0-87462-061-0 (editor) Marquette University Press, Milwaukee, 2010.
- McCarthy, Gerry. "Author Robert Ellsberg". Retrieved 2008-06-22.
- Hogan, Michael. "Quiet Gestures, Heroic Acts: A Conversation with Robert Ellsberg" Check
|url=value (help). Retrieved 2008-06-22.[permanent dead link]