In 1966 Billington appeared in Incident at Vichy at the Phoenix Theatre in London but was best known for his role as Colonel Paul Foster in the 1970 science fiction TV series, UFO, and for creating the character of Daniel Fogarty from 1971 to 1974 in the historical drama, The Onedin Line. He also appeared as Sergeant Jacko Jackson of the Royal Wessex Rangers in the series Spearhead and as Czar Nicholas II in the ITV drama series Edward the Seventh (1975).
Billington's last major TV role came in the 1986 BBC drama The Collectors, but his final appearance was in an episode of early 1990s TV series Maigret as a villain.
Billington was screen-tested for the role of James Bond more than any other actor and was said to have been Albert R. Broccoli's first choice had Roger Moore not been available (see: 1981's For Your Eyes Only). He was also screen-tested for Live and Let Die (1973), Moonraker (1979), and Octopussy (1983). Billington ultimately appeared in 1977's The Spy Who Loved Me, playing Sergei Barsov, Agent XXX's ill-fated lover, at the start of the film. His other film credits included Alfred the Great (1969) and KGB: The Secret War (1985).
Billington died of cancer at the age of 63, pre-deceasing Ed Bishop, one of his co-stars on UFO, by five days.