[3] Born in London into a theatrical family, and educated at the Nautical College Pangbourne, Cross started off by writing children's plays in the 1950s.
He achieved instant success with his first play, One More River, which dealt with a mutiny in which a crew puts its first officer on trial for manslaughter.
Another success was Half a Sixpence,[4] a musical comedy based on the H. G. Wells novel Kipps, for which he wrote the book, and for which he received a nomination for a Tony Award for Best Author.
He also wrote opera librettos for Richard Rodney Bennett (The Mines of Sulphur, All the King's Men, and Victory) and Nicholas Maw (The Rising of the Moon).
Cross later became well known for his screenplays, including Jason and the Argonauts (1963), The Long Ships (1964), Genghis Khan (1965), and Clash of the Titans (1981).