The Amulet (1979), Cold Moon Over Babylon (1980), and The Elementals (1981) were paperback original supernatural horror stories set in the South. Gilded Needles (1980), was a non-supernatural, historical horror novel dealing with a Victorian criminal family's exquisite revenge upon the family of a sternly bigoted New York judge. These were followed by his epic Blackwater (1983), a fifty-year family chronicle of a wealthy Southern dynasty with a supernatural ally, originally published in six short volumes, and the surreal Toplin (1985)

McDowell collaborated with his close friend Dennis Schuetz in writing four mysteries starring Daniel Valentine and Clarisse Lovelace. Vermillion (1980), Cobalt (1982), Slate (1984), and Canary (1986). These were published under the pseudonym Nathan Aldyne. They are light mysteries set in and around Boston and Provincetown. Daniel is a gay detective and Clarisse is a straight real estate agent and later a lawyer.

In the early 1980s, McDowell released two psychological thrillers under the pseudonym Axel Young. Both books (especially the second) were over-the-top parodies of Sidney Sheldon-type suspense novels. Blood Rubies in 1982 and Wicked Stepmother in 1983.

McDowell also wrote the novelization of the movie Clue in 1985. The movie was based on the board game and featured three different endings.

In the mid-1980s, McDowell wrote a series of light mysteries for Ballentine Books, featuring characters reminiscent of Nick and Nora Charles, originally created in Dashiell Hammett and popularized by the influential Thin Man movies. The series included Jack and Susan in 1953 (1985), Jack and Susan in 1913 (1986) and Jack and Susan in 1933 (1987). The books chronicled the adventures of an eternally youthful couple and their ever-changing dog. According to an interview, McDowell had contracted to do one for each decade of the century, but he bowed out of the contract after three.

His screen credits include Beetlejuice (1987), and collaborations on The Nightmare Before Christmas (1993) and Thinner (1996). He also wrote horror/fantasy/thriller teleplays for a number of television series.

The Amulet was meant as a motion-picture screenplay (a collaboration with one of McDowell's friends), in which the freak-accidents were contrived first, then padded with an incidental story to support them. The basic premise in the story is that of an evil, possessive woman who bequeaths a cursed necklace to a female rival neighbor. The gift brings death to anyone that receives or finds it. The bauble makes its rounds throughout the small working-class town, and eventually falls in the clutches of her much-hated ingenue daughter-in-law. Like many McDowell's novels, the setting is usually somewhere in the American south (such as Alabama).

Nathan Redfield discovers some valuable property. Unfortunately this land legally belongs to the poor but proud Larkin family who don't wish to give up their blueberry farm. Nathan resorts to murder, but regrets ever having messed with these seemingly humble, peace-loving folks.

"Katie never killed with kindness," was this paperback's tagline. Like The Amulet, a naive young woman crosses paths with a female homicidal maniac (in this case, a young hammer-wielding psychic who dispatches mother's customers requesting palmistry service). The story takes place largely in Boston, and ends in New York City.

An immigrant German family - led by matriarch Lena Shanks - exact revenge upon a Gramercy Park judge and his children. The motley Prussian characters include lesbian wrestlers who don opium-laced Thai fingernails to subdue their victims.

McDowell's most-Gothic novel, the story concerns two related Southern families joined by marriage and reunited by a funeral. The families spend a terrifying summer vacation on a jetty of land, in the Gulf of Mexico, that is cut-off from the Alabama mainland when the tide rolls in. The third Victorian house on this 'island' has remained empty and is overrun by sand-dunes. The entire resort is haunted by elemental spirits, able to control the elements (sand, water, etc.), and, in essence, reanimate dead relatives.

McDowell's "Mysterious Saga of the Caskey Family" Blackwater serial novels (6 total) consist of the following titles: The Flood, The Levee, The House, The War, The Fortune, and Rain. The series chronicles fifty-years in the lives of the Caskey family, matriarch of which is able to transmogrify into a crocodilian creature.

McDowell was born in Enterprise, Alabama. According to his bio in the 1985 edition of Toplin, McDowell lived in Massachusetts. He also maintained a residence in Hollywood with his sister Ann and adventurer-filmmaker Peter Lake. The bio described a typical day: McDowell "writes in the mornings and spends the rest of the day looking out of the window in hope that something interesting will happen" and "collects photographs of corpses". He specialized in collecting photographs of train-decapitation victims and plaques from baby caskets. McDowell's life partner of 30 years was the theatre historian and director Laurence Senelick.

McDowell died in 1999 in Boston, Massachusetts from AIDS-related illness. His unfinished novel Candles Burning was "completed" by Tabitha King, wife of Stephen King, and published in 2006.

"I am a commercial writer and I'm proud of that", he said in the book Faces of Fear in 1985. "I am writing things to be put in the bookstore next month. I think it is a mistake to try to write for the ages."