Benzion Netanyahu was born Benzion Mileikowsky in Warsaw, then part of the Russian Empire, to a Jewish family. His father was a rabbi and Zionist activist, and in 1920 took his family to the British Mandate of Palestine. It was common practice for emigrants to adopt Hebrew names after their arrival. Netanyahu attended a teachers seminary and Hebrew University of Jerusalem, where he majored in history. He specialized in the history of medieval Spanish Jews and was the author of several books, including his magnum opus, The Origins of the Inquisition in Fifteenth Century Spain (1995). In the 1930s, Netanyahu became active in the Revisionist Zionist movement and moved to New York City to serve as the personal secretary of Ze'ev Jabotinsky, the "father" of the movement. He also served as executive director of the New Zionist Organization of America. In 1944, he married Tzila Segal, and the couple had three sons, including future Israeli Prime Minister Benjamin Netanyahu. Following Israel's declaration of independence in 1948, Netanyahu returned to Israel and became the chief editor of the Encyclopaedia Hebraica. In 1957, he went back to the USA to teach in the Hebrew Language Department of Dropsie College in Philadephia and the Hebraic Studies Department of the University of Denver. Later he became a professor of Judaic Studies at Cornell University.
In the late summer of 1976, the family returned to live in Israel permanently.