Hart began his career as a reporter in Central Africa, on the Nyasaland Times, and served as a war correspondent in Vietnam. He tells of having been the first Western correspondent to reach the banks of the Suez Canal with the Israeli army in 1967. He also tells of having been friendly with both Golda Meir and Yasser Arafat at roughly the same time and having been on friendly terms with such leaders as Saudi Arabia's King Faisal, Jordan's King Hussein, and both Egyptian presidents Nasser and Sadat.
Hart says he was told by his editor Geoffrey Cox early in his career, "Never forget that leaders are the most lonely people in the world because they are surrounded by sycophants who only tell them what they want to hear. They, the leaders, are crying out for honest conversation." Inspired by this advice, he says, he held "private one-on-one conversations over the years with leaders on both sides of the Arab-Israeli connection, giving him a rare insight into the truth of what they really believed and feared as opposed to what they said in public for propaganda and myth-sustaining purposes."
In 1973 Hart addressed global poverty with a two-hour film titled "Five Minutes to Midnight." Its world premiere was hosted by Secretary General Kurt Waldheim at the opening of the 7th Special Session of the UN General Assembly that had been called to discuss a new world economic order.
Hart was involved in the failed attempt by the late Shah of Iran to go into exile in the UK after he was deposed from power. On 9 February 1979, as a freelance journalist close to the Shah, Hart contacted Downing Street to say the deposed royal was interested in living full-time at his lavish estate in Surrey, southwest of London.
Hart also tells of having been the unofficial linkman in a secret exploratory dialogue between Arafat and Shimon Peres in 1980.
Hart has never been a member of any political party or group. When asked what drives him he has said, "I have three children, and, when the world falls apart, I want to be able to look them in the eye and say, "Don't blame me. I tried."