Byrne's other works include the novel Groupie (1969, co-written with Jenny Fabian), the BBC "Wednesday Play" Season of the Witch (1971), and the scripts for the films Adolf Hitler: My Part in His Downfall (1972, co-written with original author Spike Milligan and Norman Cohen), and Rosie Is My Relative (1976).

[2] Byrne was the most prolific scriptwriter for the first series of Space: 1999 (1973–75), and was initially assigned the role of creative consultant for the second season (1976–77).

However, hoping to make a greater impact on the American market, the producers desired a consultant from the United States, and the job was subsequently given to Fred Freiberger.

Byrne's scripts for series one of Space: 1999 were "Matter of Life and Death" (based on a draft by Art Wallace), "Another Time, Another Place", "Force of Life", "Voyager's Return" (based on an idea by Joe Gannon), "End of Eternity", "The Troubled Spirit", "Mission of the Darians", and "The Testament of Arkadia".

Byrne's second story, Arc of Infinity (1983), featured the Time Lord villain Omega, who had first appeared in The Three Doctors a decade earlier.