James Cross was born 29 September 1921, the son of J. P. Cross and Dinah Cross (née Hodgins); he was educated at King's Hospital Dublin and Trinity College, Dublin (Scholar, First Class. Moderatorship Economics and Political Science). In 1945 he married Barbara Dagg.
After serving as a Lieutenant in the Royal Engineers, Cross began his Civil Service career as Assistant Principal, Board of Trade in 1947. His later positions included: Private Secretary to Parliamentary Secretary, 1947-49; Principal, 1950; Trade Commissioner: New Delhi [India], 1953-56; Halifax [Canada], 1957-60; Winnipeg, 1960-62; Assistant Secretary, 1962; Senior Trade Commissioner, Kuala Lumpur [Malaysia], 1962-66; Board of Trade, 1966-67; Under Secretary, 1968; Senior British Trade Commissioner, Montreal, 1968-70 (kidnapped by terrorists and held for 59 days, October-December 1970); Under-Secretary, Export Planning and Development Division, Department of Trade and Industry, 1971-73; Secretary, British Overseas Trade Board, 1972; Coal Division, DTI, later Department of Energy, 1973-78; Under-Secretary, Principal Establishment Officer, Department of Energy, 1978-80.
He was awarded the CMG in 1971.