Gerald Seymour was born in Guildford in 1941 to a literary family. He was educated at Kelly College at Tavistock in Devon and took a BA Hons degree in Modern History at University College London. In 1963 he joined ITN and his first assignment was reporting on the aftermath of the Great Train Robbery. Within a year, he had been sent to Cyprus, where he covered his first military conflict. For the next 15 years he reported from areas of conflict around the world from the front-line in South Vietnam, to Aden to Pakistan to Northern Ireland. He became a specialist in terrorism, reporting on the Basque campaign in northern Spain, the Red Army faction in West Germany, the Red Brigades in Italy, the Angry Brigade in Britain and the worldwide attacks by Palestinian groups. .

In 2001, Seymour was the only journalist featured in the Oscar-winning television film, One Night in September, which told the story of the killing of the Israeli athletes and team members at the Munich Olympics. He and his ITN team had the closest proximity to the events of that day. From 1969, he spent a good deal of time in Northern Ireland and this experience formed the basis of Harry's Game, an immediate bestseller and later an acclaimed TV series. He stayed with ITN until 1978, spending the last two years running their Rome office. During this time he had written two more novels and decided to write full time. For six years he and his family lived in Ireland, returning to settle in the West Country in 1984.