Kenneth Lonergan, director of “Manchester by the Sea.” (Marvin Joseph/The Washington Post)

There’s an early scene in Kenneth Lonergan’s “Manchester by the Sea,” a grief-drenched drama starring Casey Affleck and Michelle Williams, that effectively announces to viewers that the ensuing movie won’t hew to the usual rules of multiplex ma­nipu­la­tion: Affleck’s character, a Boston handyman named Lee Chandler, has received an emergency call to travel to his titular home town, where he proceeds directly to the hospital where someone close to him has died.

The scene in question, during which Lee consults with a doctor and a nurse during a conversation in a hallway, unfolds in real time, as he processes the most mundane details of death — logistics, lists, arrangements — with hushed, workmanlike focus.

It’s the kind of sequence that would be quickly excised in most movies, to get to what most filmmakers assume the audience wants, in the form of a big speech or juicy crying scene. But it’s precisely the kind of moment — subdued, interstitial, not conventionally exciting but teeming with life and buried emotion — that makes a Kenneth Lonergan film unlike any other.

“I’ve been in those hallways a few times, and you don’t get out of them quick enough,” the filmmaker explained in September, before “Manchester by the Sea” was set to screen at the Toronto International Film Festival. To him, such everyday encounters are “gold mines” of human drama and unspoken meaning. “If you just swipe away all those mundane details, you have to provide what’s often a very false conflict,” Lonergan explained, adding that it’s often a “very easy conflict that you’ve seen a million times. The first time the couple meets and they’re going to fall in love, first they’re really snarky with each other and competitive, and they put each other down. [But] most girls I ended up with I got along pretty well with from the beginning. The tensions came from other things. And those tensions are there for anyone to mine who wants to pay attention.”

Paying attention is a good word for what Lonergan, 55, has done so preternaturally well throughout his career. He grew up in New York, the son and stepson of psychoanalysts (his father is a physician); he became best friends with the actor Matthew Broderick when the two attended a progressive private school in Manhattan, where they honed their observations of human nature while sharing the occasional joint in Central Park. After writing the enthusiastically received 1996 off-Broadway play “This Is Our Youth,” starring an unknown actor named Mark Ruffalo, ­Lonergan’s gifts were quickly co-opted by Hollywood, where he wrote the Robert De Niro comedies “Analyze This” and “The Adventures of Rocky & Bullwinkle,” and worked on Martin Scorsese’s “Gangs of New York.” It was under Scorsese’s banner that Lonergan wrote and directed the 2000 drama “You Can Count On Me,” which starred Laura Linney, gave Ruffalo his first breakout movie role and announced a thrilling new filmmaking voice in Lonergan, whose alternately funny and melancholy insights into the ways people speak, behave and navigate ­psychosocial minefields earned him an immediate and ardent cult following among audiences and actors alike.

‘He trusts himself’

Casey Affleck in “Manchester by the Sea.” (Claire Folger/Amazon Studios/Roadside Attractions )

Casey Affleck and Kenneth Lonergan on the set of ”Manchester by the Sea.” (Claire Folger/Amazon Studios/Roadside Attractions)

“It’s like you’re eavesdropping,” said Michelle Williams of reading a typical Lonergan script. “You feel like you have like a hidden camera on these people’s lives, so as you’re reading it, you can see the whole thing, totally unbroken.” Affleck concurred. “It feels like nothing’s happening,” he said. “So many of the scenes have a lot of conflict in them, but the conflict is almost never about what the movie’s about in any way. It’s always people arguing about, Did you put the food in the freezer, Where are the car keys, all this stuff. And in some cases, with a different writer, that’s all it would be about. It wouldn’t add up to anything. It would be a slice of life. In this case, you’re following these people and their sometimes petty conflicts, sometimes bigger problems, but you never feel like you’re being led. Then at the end, you do arrive somewhere, and you feel like you got there on your own, but you didn’t.”

Affleck, whose haunted, powerfully affecting performance in “Manchester by the Sea” has earned him early front-runner status in the Oscars race, wasn’t initially supposed to be in the film, which was conceived by producers Matt Damon and John Krasinski as a project for Damon to direct and star in; Lonergan was contracted to write the script.

Damon’s schedule eventually led him to cede directing duties to Lonergan, who a few years earlier had endured one of the most exhausting periods of his career, when his sophomore film, “Margaret,” became entangled in a nasty creative, legal and financial dispute with financier Gary Gilbert, who took issue with how long Lonergan took to edit the film, and was unhappy with the final product, going so far as ordering his own edit of the film and suing Lonergan for breach of contract. (After six years of wrangling, Gilbert’s case against Lonergan was finally dismissed in 2014.)

Although “Margaret” was hailed as a masterpiece when it finally received a small theatrical release in 2011, Broderick, who has appeared in all three of Lonergan’s films, noted that “it wasn’t so clear” that his friend would be given another chance to direct. “He was in a lot of trouble,” Broderick recalled. “A lot of people were very mad at him.” Calling “Manchester” an “amazing comeback,” he added that Lonergan never lost confidence in his own voice. “He’s had that since he was a teenager,” he said. “There’s a level there where he’s just sure of himself. He trusts himself at some deep level.”

Lonergan bristles at the notion that “Manchester by the Sea” is a comeback — he wrote and directed two plays in the intervening years, after all, as well as an adaptation of “Howard’s End” for the BBC. “I wasn’t that bruised,” he insisted. “I was tired.” Still, he admitted dryly, “it’s nice to have people paying attention to me and complimenting me instead of yelling at me. It’s much better.”

Lonergan is a notorious whinger on the set, freely admitting how less than thrilled he is with the day-to-day process of directing. But, in terms of scope and structure, “Manchester by the Sea” reflects growing ease with a medium that he seems finally to have made his own, albeit warily. “I definitely feel like I’m a director now,” Lonergan said flatly. “There’s the scheduling and the workflow of moviemaking, and the number of people involved, and all that’s a managerial issue that I could certainly stand to improve for myself. But the actual multiple facets of filmmaking are starting to really open up for me creatively, and I’m very interested in them now. I no longer feel like a writer who directs.”

Affleck guffawed when he was apprised of Lonergan’s change of heart. “Oh, yeah?” he said, laughing. “Oh, I’m going to text him about that one. I’m glad he says that, he’s so self-deprecating all the time. He’s like, ‘I hate this, I’m never going to go on a movie set again, I probably won’t see another movie.’”

Echoing Affleck’s skepticism, Broderick confirmed that Lonergan “was bitching all the time” while filming “Manchester by the Sea.” But he demonstrated newfound confidence as well. “I noticed he didn’t do as many takes or cover as much as he did in ‘Margaret.’ He moved along more easily.” Lonergan’s willingness to claim the mantle of director, he noted, might have something to do with the near-universally ecstatic praise that “Manchester by the Sea” has received since premiering at Sundance in January. “That said, there’s something about Kenny that no matter what people on the outside say, he stays true to himself. He keeps his grumpiness and his own voice, whether people are going crazy loving his things or not so much.”

For now, the “going crazy” vote seems to be far outpacing “not so much,” as “Manchester by the Sea” arrives in theaters, and a growing number of filmgoers are introduced to a director who may not give them what they’ve been taught to expect, but instinctively knows exactly what they need by way of an emotional connection that can be tough, but also tender at the bone.

“I just don’t know what the audience wants, so I have to assume they want what I want,” Lonergan explained. “I have no other guide.”