Rabbi Gellman is the senior rabbi of Temple Beth Torah in Melville, New York, where he has served since 1981.

After receiving a B.A. from the University of Wisconsin in Madison with a major in Hebrew and Semitic studies in 1969, he completed his studies at the Hebrew Union College-Jewish Institute of Religion by 1971. He was ordained by the college institute in 1972 and was awarded the senior homiletics prize. He was the youngest rabbi ever ordained by the seminary and completed the five-year program in two years of residency.

Rabbi Gellman received his Ph.D. in Philosophy from Northwestern University in 1981 and has taught at Antioch College, HUC-JIR New York, Northwestern University, Princeton University, Mt. Sinai Hospital, and other academic institutions. Rabbi Gellman served as chairman of the Medical Ethics Committee of the UJA Federation of New York and is a contributor to its Compendium of Jewish Medical Ethics. He has published widely and has contributed to a recent Commentary Magazine symposium on the state of Jewish belief. He also writes for Golf Digest, is a contributing editor to Moment Magazine, and has authored several children's books.

In addition to regular television appearances, Rabbi Gellman has served as chairman of the UJA rabbinical advisory committee, founding chairman of the Long Island Rabbinical Advisory Council, and president of the New York Board of Rabbis. He is the recipient of many awards, including the Tzedaka Award from the UMA-Federation and the Moshowitz Award for rabbinic excellence from the NYBR.

On November 12, 1998,he was a panelist at the Connecticut Forum, Brave New World or Return of Frankenstein?