Robert is the son of the American military analyst and whistleblower, Daniel 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.

Robert returned to Harvard, and earned a degree in religion and literature, and later a Master's in Theology from Harvard Divinity School.

In 1987 he began work as editor-in-chief of Orbis Books. He in 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 currently resides in Ossining, New York with his wife and their three children."Robert Ellsberg." Our Authors. The Crossroad Publishing Company. 8 Feb. 2008