Shia LaBeouf, right, stars in “Lawless” as Jack Bondurant, the youngest member of a moonshine-running family from Virginia.

In his novel “The Wettest County in the World,” Matt Bondurant wrote some pretty violent passages. But it wasn’t until his book became the movie “Lawless,” out Wednesday, that he realized what his words had really depicted — especially in a story in which nearly every character likes to stab, shoot and/or slice his enemies whenever he gets the chance.

For one scene in particular, when one character gets his throat sliced from end to end, the moving pictures really bring what happens on the page to life. “There’s a big splash of blood. There’s an immediate repulsion,” Bondurant says. “I was practically hiding my eyes, and I knew what was coming. I wrote the thing!”

Both Bondurant’s book and the movie — which stars Shia LaBeouf, Tom Hardy and Guy Pearce — tell the lightly fictionalized story of Bondurant’s grandfather and great-uncles, who were moonshine runners in Franklin County, Va. LaBeouf plays Jack, the youngest Bondurant, who wants to achieve success beyond what his older brothers can imagine. Guy Pearce is a crooked FBI agent out to shut down the Bondurant operation, and Gary Oldman has a small role as a big-city moonshiner.

The novel was optioned for the screen even before it hit shelves, but that’s never a guarantee that a movie will get made. “So many books get bought, and I know some people personally who have [sold the movie rights] and they’ve been bouncing around L.A. for a long time,” Bondurant says. “Of course, [having the film finally get made and released] is somewhat flattering, but I didn’t believe it was definitely going to happen.”

When the production company brought Bondurant and his father to the Georgia set, things started to get more real. “They say, ‘Until they say action, nothing is definite,’ but when I saw all the stuff they had done, then at that point it’s really happening.”

Bondurant had nothing to do with the making of the film, other than writing the novel — screenwriter (and musician) Nick Cave was given the task of translating the book to the screen. Cave made some cuts, including excising entirely the narrator of Bondurant’s book. Bondurant doesn’t mind, though, and in fact sees Cave’s adaptation as almost a natural extension of the writing process.

“There’s a kinship, or understanding of [the filmmakers’] process,” he says. “I already did things to [the Bondurant family]; I fictionalized some elements. Now [the film is] just sort of taking it to another level.”