Kopal was born and grew up in Litomyšl (Czechoslovakia, now Czech Republic). In his early astronomical career, he studied variable stars and in particular close eclipsing binary stars. He attended Cambridge University in 1938 and later that year he went to Harvard College Observatory. After the war he became head of the astronomy department at the University of Manchester. He later assisted NASA with the Apollo program as an external expert.
He was Editor-in-Chief of the journal Astrophysics and Space Science since its foundation in 1968 until his death in 1993.