[5] His hometown inspired the fictional town of New Zebedee, Michigan, where he set his trilogy about Lewis Barnavelt and Rose Rita Pottinger.

[6] Shy, overweight, and often bullied as a child, he had become a voracious reader and a self-described "bottomless pit of useless information" by the time he graduated from Marshall High School[7] and entered the University of Notre Dame in 1955.

His personal interests included archaeology, architecture, history, Latin, baseball, kitschy antiques, bad poetry, visits to the UK, and trivia of all kinds.

[11] Bellairs' first published work, St. Fidgeta and Other Parodies (1966), is a collection of short stories satirizing the rites and rituals of Second Vatican Council-era Catholicism.

The following year, the hagiography of St. Fidgeta was supplemented by eleven other humorous stories, including an essay on lesser-known popes of antiquity, a cathedral constructed over the course of centuries, and a spoof letter from a modern-day Xavier Rynne about the escapades at the fictional Third Vatican Council.

[21] An unfinished sequel titled The Dolphin Cross was included in the anthology Magic Mirrors (New England Science Fiction Association Press, 2009).

[22] Following the success of The House with a Clock in Its Walls, Bellairs focused on writing Gothic fantasy adventures aimed at elementary and middle-school children.

"I love haunted houses, ghosts, witches, mummies, incantations, secret rituals performed by the light of the waning moon, coffins, bones, cemeteries and enchanted objects.

"[3] Bellairs also wrote his hometown influenced his creative bent: “In my imagination I repeatedly walk up and down the streets of the beautiful old Michigan town where I grew up.

It’s full of old Victorian mansions and history, and it would work on the creative mind of any kid.”[7] Writing for The New York Times, Marilyn Stasio characterized Bellairs' children's books as fast-paced, spooky adventures involving "believable and likeable" characters, generally a child and an older person (usually a "lovable eccentric")[24] who are friends and must go on adventures and solve a mystery involving supernatural elements such as ghosts and wicked sorcerers.

Beyond these supernatural elements, Bellairs's novels evoked "a child's concern with comfort and security in his real world," addressing childhood fears of abandonment, loneliness, and bullying, as well as coming of age.

The Bellairs estate commissioned Brad Strickland to complete the two unfinished manuscripts and to write novels based on the two one-page outlines.

[22][25][26] Professor Gary D. Schmidt contended that Bellairs' Lewis Barnavelt and Rose Rita Pottinger trilogy traced the "emerging acceptance of self" by the two main characters, who struggled with internalized gender norms.

[22] Conservative critic William Kilpatrick observed of Bellairs that "While his books are quite frightening, they are well written and undergirded by a moral vision" and recommended them to parents who wish to expose their children to age-appropriate literature that both entertains and edifies.

[30] Educators have used The House With the Clock in Its Walls as a case study for using storytelling techniques to draw in reluctant readers[31] and assigned The Curse of the Blue Figurine to students in a book club.

Marilyn Fitschen provided the covers and illustrations for Bellairs' first three books: St Fidgeta and Other Parodies, The Pedant and the Shuffly, and The Face in the Frost.

As a company, we aspire to be a haven for artists and friends who believe in the power of myth and remember that feeling we all got as kids, when the lights went down and the images came up and anything was possible.”[35]The film adaptation of Bellairs' novel The House with a Clock in Its Walls stars Jack Black as Uncle Jonathan, Cate Blanchett as Mrs. Zimmerman, and Owen Vaccaro as Lewis Barnavelt, and was directed by Eli Roth.