Katz was born in
Johannesburg, South Africa. His parents were Alexander and Luba Katz. In 1930, he joined the
Betar movement. In 1936, Katz
immigrated to
Mandatory Palestine as the secretary of Michael Haskel, the South African honorary consul. Soon after his arrival, he joined the
Irgun. In 1939, he was sent to London by
Ze'ev Jabotinsky to speak on issues concerning Palestine. While there he founded the
revisionist publication
The Jewish Standard and was its editor, 1939 to 1941, and in 1945. In 1946, Katz returned to Mandatory Palestine and joined the HQ of the Irgun where he was active in the aspect of foreign relations. He was one of the seven members of the high command of the Irgun, as well as a spokesman of the organization. Katz also served as Irgun commander in
Jerusalem during the War of Independence.
Menachem Begin writes in
The Revolt that Katz "was the officer responsible for Jerusalem until the dissolution of the military regiments of the Irgun Zvai Leumi." ==Political career==