Kenneth Lonergan made a memorably acclaimed directing debut in 2000 with the film “You Can Count on Me,” a deft, observant, funny-sad drama-comedy starring Laura Linney and Mark Ruffalo. The film, about a brother and sister reuniting after a period of estrangement, was nominated for two Oscars, landed on several critics’ top-10 lists and seemed to assure Lonergan — already a celebrated New York playwright — a long and happy career in the movie business.

Five years later, Lonergan was behind the camera again, on New York’s Upper West Side, with an urban coming-of-age drama called “Margaret.” He had reconvened many of his rep players from “You Can Count on Me,” including Ruffalo, Matthew Broderick, Kieran Culkin and Lonergan’s wife, J. Smith-Cameron. Anna Paquin had been cast in the film’s leading role, a 17-year-old high school student named Lisa whose life is upended after she witnesses a horrifying accident.

With such an accomplished ensemble of players; a textured, philosophically deep story about a young woman’s loss of innocence; and such high-powered executive producers as the late Sydney Pollack and Anthony Minghella, as well as the formidable Scott Rudin, Lonergan’s “Margaret” seemed on its way to becoming as admired a sophomore effort as “You Can Count on Me” had been a dazzling debut.

But, after the requisite months-long editing period, “Margaret’s” expected arrival at Sundance, Cannes or Telluride failed to materialize. One year, then two, then three went by, with no sign of the film on the horizon. Fox Searchlight, the studio that co-financed “Margaret,” kept mum on the subject.

In 2008, stories began to surface that Lonergan was having trouble finishing the film; in 2009, the Los Angeles Times reported that the project had “turned into a nightmarish production that has devolved into a bitter court fight,” the subject of not just one but two lawsuits. (According to the Times, Fox Searchlight sued producer Gary Gilbert for failing to pay half the production costs; Gilbert in turn sued both Searchlight and Lonergan, claiming they blocked his efforts to help finish the movie and forced him to pay for an “inferior and unmarketable” film.)

The good news is that “Margaret” has finally made it to theaters (it opens Friday at the West End Cinema). The bad news is that, because of ongoing legal action, Lonergan can’t speak in detail about why his film took so long to get here. “I just say it took a long time,” he said earlier this week, calling from his parked car in New York’s Greenwich Village. “It’s not a very interesting answer, but sometimes it takes a while for these things to get settled, and to get to a place where everyone’s happy.”

Although “Margaret” took seven years to make it to the screen, the story actually began more than 30 years ago, when Lonergan and Broderick were classmates at the Walden School, a progressive private high school on the Upper West Side that closed in the late 1980s. Many of “Margaret’s” most searing — and amusing — scenes take place in and around a fictionalized version of Walden, where Lisa and her classmates get into impassioned arguments about everything from the Middle East to “King Lear.” Broderick plays a mild-mannered English teacher and Matt Damon plays a hunky geometry teacher with whom Lisa develops a confiding relationship.