Born in South Philadelphia, Unterberger survived bouts with scarlet fever and then rheumatic fever as a small child. The latter disease left him with a heart condition that restricted his physical activity until high school.
While that made him ineligible for military service during World War II, the condition eventually dissipated; by the time he entered college, he was able to participate in normal physical and recreational activities. In 1944, he graduated from the University of Pennsylvania, and then from Penn's law school in 1948. He joined his father's firm, and was admitted to the Pennsylvania State Bar in 1949.
Specializing in real estate law, he practiced with several firms, including Gold, Bowman & Korman; Pechner Dorfman; and Pelino & Lentz. He also practiced corporate and estate law to accommodate his real estate clients as their businesses grew.
Unterberger was admitted to practice before the U.S. Supreme Court in 1961. He received a commendation for 50 years of law practice from the Philadelphia Bar Association on June 23, 1999.
In addition to his longstanding membership at Har Zion, he was active in other areas of the Jewish community. He was a charter member of B'nai B'rith's William Portner Lodge, serving as its seventh president in 1955-56. In 1990, he became editor of the lodge's publication, The Town Crier, printed by his brother-in-law and close friend, Martin Piltch. After it ceased to be in 1999, he and Piltch continued to issue it as a two-page newsletter until 2009.
He is survived by his wife of 59 years, the former Suray Chernick; sons Glenn Unterberger, Howard Unterberger, Steve Unterberger and Richie Unterberger; sister Rhoda Piltch; and four grandchildren.