His series of macabre films include House of Dark Shadows, Night of Dark Shadows, The Night Stalker (for many years holding the record ratings of the most-watched TV movie—and inspired the series Kolchak: The Night Stalker), Intruders, The Night Strangler, Burnt Offerings, Trilogy of Terror, The Norliss Tapes (a 1973 pilot for an unproduced series starring Roy Thinnes), Curse of the Black Widow, Dead of Night, Scream of the Wolf and others. He worked frequently with sci-fi/horror writer Richard Matheson. Curtis was producer and/or director of a number of television adaptations of horror-related productions including The Strange Case of Dr. Jekyll and Mr. Hyde (1968), Dracula (1973), Frankenstein (1973), The Picture of Dorian Gray (1973), and The Turn of the Screw (1974).
In 1978, Curtis made a departure from his usual macabre offerings, when he wrote, produced, and directed the sentimental NBC television film When Every Day Was the Fourth of July. Although fictionalized, the film was semi-autobiographical, based on his childhood growing up in Bridgeport, Connecticut in the 1930s. The film was originally intended to be a pilot for a potential series, but when the series was not picked up by the NBC network, Curtis produced and directed the 1980 television movie sequel The Long Days of Summer, this time airing on the ABC network.
His 1983 miniseries The Winds of War was nominated for four Emmy Awards.
He also directed the War and Remembrance mini-series which was the continuation of The Winds of War. This mini-series was 30 hours in length and was split into two segments. Chapters I-VII aired in November 1988. The remaining five parts, Chapters VIII-XII, were billed as "The Final Chapter", and aired in May 1989. This series received 15 Emmy Award nominations and won for best miniseries, special effects and single-camera production editing. The miniseries was nominated for Emmy Awards for best actor (John Gielgud), actress (Jane Seymour), supporting actor (Barry Bostwick) and supporting actress (Polly Bergen). The New York Times profiled him while in post-production on War and Remembrance.
Curtis' rights to Dark Shadows remain with his estate, which signed a deal with Warner Bros. for a new Dark Shadows movie. The film stars Johnny Depp as Barnabas Collins and was released in May 2012.