James White was born in Belfast, Northern Ireland, on 7 April 1928, and spent part of his early life in Canada. He was educated in Belfast at St. John's Primary School (1935 – 1941) and St. Joseph's Technical Secondary School (1942 – 1943). As a teenager he lived with foster parents. He wanted to study medicine but financial circumstances prevented this. Between 1943 and 1965 he worked for several Belfast tailoring firms and then as assistant manager of a Co-op department store. He married Margaret ("Peggy") Sarah Martin, another science fiction fan, in 1955 and the couple had three children: daughter Patricia, and sons Martin and Peter. White later worked for the aeroplane builders Short Brothers Ltd. as a technical clerk (1965 – 1966), publicity assistant (1966 – 1968), and publicity officer (1968 – 1984).
He became a science fiction fan in 1941, attracted particularly by the works of E. E. "Doc" Smith, which featured good aliens as well as evil ones, and of Robert A. Heinlein, many of whose stories center round ordinary people. In 1947 he met another Irish fan, Walter A. Willis (1919 – 1999), and the two helped to produce the magazines Slant (1948 – 1953) and Hyphen (1952 – 1965), which featured stories and articles by noted authors including John Brunner, A. Bertram Chandler, and Bob Shaw. In 2004 both White and Willis were nominated for the retrospective Hugo Award for Best Fan Writer of 1953, although neither won.