After graduating from New York University, Kadushin studied for the rabbinate at the Jewish Theological Seminary of America during the 1920s. There he encountered Mordecai Kaplan and soon became a key figure in Kaplan's Reconstructionist Judaism movement. As his studies in haggadah continued during the late 1920s, however, he found himself drifting away from Kaplan's decidedly modernist approach to rabbinics and began to argue for a more aftermodernist approach—one that placed greater weight on the enduring significance of the haggadah.
In 1921, Kadushin became the rabbi of Congregation B'nai Israel of Washington Heights in New York City. In 1923 he married Evelyn Garfiel, a psychologist and professor, who later became well known for her book on Jewish prayer, The Service of the Heart (1958). Their son, Charles Kadushin, became a notable sociologist and social network analyst at Columbia University and later, the Graduate Center of the City University of New York.
In 1926, Kadushin moved to Chicago, where he became the rabbi of Humboldt Boulevard Temple. In 1931, Kadushin moved to Madison, Wisconsin, where he served as the rabbi of the University of Wisconsin Hillel. In 1932, he received a Doctor of Hebrew Letters degree from the Jewish Theological Seminary.
From 1942 to 1952 he was director of the Hebrew High School of Greater New York, later known as the Marshaliah Hebrew High School. During the next several years he served two congregations in the New York area, the Bay Shore Jewish Center of Long Island, 1953–1954, and Synagogue Adath Israel of Riverdale, Bronx, New York, 1954-1958. From 1958 to 1960 Kadushin was professor of midrash and homiletics at the Academy for Higher Jewish Learning in New York City.
In 1960 Kadushin was invited to become visiting professor in ethics and rabbinic thought at The Jewish Theological Seminary. He held this position from 1960 to 1980, the year of his death.
Kadushin is now regarded as an important figure in the history of twentieth-century Conservative Judaism. In 1990, the book, Teaching for Christian Hearts, Souls & Minds, written by the Rev. Locke E. Bowman, Jr., after conversations with one of Kadushin's students, Rabbi Arnold Resnicoff, was an attempt to apply Kadushin's theories of value concepts and organic Judaism to Christian teaching.
 "The Theology of Seder Eliahu" (1932)
This work, a commentary on Seder Eliahu, was derived from Kadushin's Ph.D. dissertation. In it, he argues that ancient rabbinic texts possess organic, experiential consistency despite the sometimes non-linear character they possess.
 "Organic Thinking" (1938)
Generally regarded as Kadushin's most important work, this volume establishes the fundamentals of Kadushin's philosophy--value-concepts, indeterminacy of belief, and normal mysticism—in a relatively straightforward manner. Although much of the work consists of textual analysis, the influence of Alfred North Whitehead is more apparent in this volume than in any of Kadushin's other works.
 "The Rabbinic Mind" (1952)
 "Worship and Ethics" (1964)
This volume focuses primarily on rabbinic moral theology and Jewish mysticism. It is notable, among other reasons, for Kadushin's relative denunciation of Kabbalah as a tradition with which traditional rabbinic philosophy cannot easily be reconciled. Kadushin sees more practical value in normal mysticism, the complex but decidedly non-supernatural everyday religious experience of any pious and observant Jew.
 "A Conceptual Commentary on the Mekilta" (1969)
 "A Conceptual Commentary on Midrash Leviticus Rabbah" (1987)
These two volumes represent Kadushin's efforts to apply his system of hermeneutics to classic rabbinic texts.
"What is not defined usually cannot be defined." 
"Torah is not only personified, but possesses the quality of a personality."
"[S]piritual experience in most religions is seldom an unmixed blessing. Left to itself, uncontrolled, it may manifest itself in the most absurd of human vagaries and sanctify not only unsocial but anti-social behavior and utterly callous selfishness."
- Teaching for Christian Hearts, Souls & Minds, Locke E. Bowman, Harper and Row, 1990.
- The Rabbinic Mind, p. 45.
- Organic Thinking, p. 17.
- Organic Thinking, p. 59.