Space: 1999 portrayed a future of international space exploration, and the British series tried to reflect that with international cast (and some international crew).
- Martin Landau (John Koenig).
- Barbara Bain (Helena Russell).
- Kathryn Leigh Scott (Yesta, Dorzak)
- Alibe Parsons (Alibe)
- Karl Held (Jerry Travis, The Immunity Syndrome).
- Hal Galili (Voice, The Immunity Syndrome)
- Marc Smith (Cloud Voice, The Beta Cloud
- Bob Sherman (newscaster, Dragon's Domain)
- Don Fellows (newscaster, Breakaway)
- Stuart Damon (Parks, Matter of Life and Death, Guido Bringers of Wonder)
- Richard Le Parmentier (Sam Malcolm, Dorzak)
- Jill Townsend (Sahala, Dorzak)
- George Bellak was story consultant during early development.
- Abe Mandell was president of ITC and closely involved with the production.
- Lee H Katzin directed Breakaway and Black Sun
- Writer Art Wallace (Siren Planet)
- Writer Jesse Lasky Jnr was an American writer resident in Britain who wrote The Full Circle
- Fred Freiberger (Year 2 producer/ writer).