He went on to earn a degree in law at University College London and then qualified as a barrister at Lincoln's Inn. He joined the British army during World War II, operating primarily in Germany as a tank commander in the Armoured Division. There, he was given his lifelong nickname of "Vivian" because the British could not pronounce the name, "Chaim". A Jewish soldier had volunteered that "Vivian" was the English equivalent of "Chaim." (Living History, p. 47) He was commissioned into the Intelligence Corps in 1943 and participated in the liberation of several concentration camps as well as identifying a captured German soldier as Heinrich Himmler. He left the Army in 1947 with the rank of Major.
After leaving the army, Herzog opened a private law practice. He returned to public life in 1967, when the Six-Day War broke out, as a military commentator for Kol Israel radio news. Following the capture of the West Bank, he was appointed Military Governor of East Jerusalem, and Judea and Samaria.
In 1975 Herzog was appointed Israel's Ambassador to the United Nations, in which capacity he served until 1978. During his term the UN adopted the "Zionism is Racism" resolution (General Assembly Resolution 3379), which Herzog condemned and symbolically tore up (as his father had done to one of the British white papers regarding the British Mandate in Palestine), saying: "For us, the Jewish people, this resolution based on hatred, falsehood and arrogance, is devoid of any moral or legal value."
In 1983 he was elected the sixth President of Israel by the Knesset; he served two five-year terms (then the maximum permitted by Israeli basic law), retiring from political life in 1993. As president of Israel, Herzog made a number of visits abroad, being the first Israeli president to make an official visit to Germany, as well as visiting several far-east countries, Australia, and New Zealand. He was also noted for pardoning the Shin Bet agent involved in the Kav 300 affair.
In 1985 Herzog visited Wesley College Dublin during his State Visit to Ireland, during which he opened the Irish Jewish Museum in Dublin.
Herzog controversially reduced the sentences of three imprisoned Jews, Menachem Livni, Uzi Sharbaf and Shaul Nir, members of the Jewish Underground, who were sentenced to life imprisonment in 1985 for the 1984 murder of four Palestinians in the West Bank town of Hebron. Herzog had reduced the sentences, first to 24 years, then to 15 years, and in 1989 he reduced the sentence to 10 years, which enabled the men to be released two years later on good behavior..
Herzog was the brother-in-law of Abba Eban; the men's wives were sisters. He had three children, including Isaac Herzog, currently (2006-) Minister of Social Affairs, Minister of the Diaspora, and a Knesset Member for the Labour Party.
Herzog also authored several books on the historical events in which he was involved, including: