He became known in North America and Europe in the 1960s for his work on ecumenism, interfaith dialogue, and the relationship between the Catholic Church and Jews.
In the later 1960s, he went to the New School for Social Theory in New York and became a sociologist, which led to his work on creating a dialogue between classical sociology (Marx, Tocqueville, Durkheim, Toennies, Weber, etc.)
In the 1980s and 1990s, Baum continued his study into ideology critique by integrating the work of the Frankfurt School of Critical Theory.
He connected the Frankfurt School's concept of "the end of innocent critique" with Liberation theology's "preferential option for the poor".
While they may not be sure of the theological grounds that dispense them from this mission, the churches have become aware that asking the Jews to become Christians is a spiritual way of blotting them out of existence and thus only reinforces the effects of the Holocaust.
Canadian author Michael Higgins, who first met Baum in 1968, writes "Politeness, ingenuousness, and collegiality are the personal as well as professional qualities that have defined his life and vocation no matter the setting — university, chancery, parish hall, retreat house, or activist cell.
In 1990, he was made an Officer of the Order of Canada in recognition of being "a guide and inspiration to generations of students of many different faiths and backgrounds".