Rabbi Herzog served as rabbi of Belfast from 1916 to 1919 and was appointed rabbi of Dublin in 1919. A fluent speaker of the Irish language, he supported the First Dáil and the Irish republican cause during the Irish War of Independence, and became known as "the Sinn Féin Rabbi". He went on to serve as Chief Rabbi of Ireland between 1922 and 1936, when he immigrated to Palestine to succeed Rabbi Abraham Isaac Kook as Ashkenazi Chief Rabbi upon his death. He became a supporter of both the Irish Republican Army and the Irgun.