Kenneth Lonergan can claim responsibility for a Pulitzer Prize­­–nominated play (The Waverly Gallery), an animated box-office bomb (Rocky and Bullwinkle), two Academy Award screenwriting nominations (for You Can Count on Me and Gangs of New York), one of the most divisive art-house films of the past decade (Margaret), and an episode of the beloved Nickelodeon television series Doug: a wide variety of projects, all of which seem to produce in him a mix of equal parts excitement and anxiety.

In college, I directed a production of This Is Our Youth, Lonergan’s hilarious and heartbreaking play about wealthy and lost New York City teenagers, which premiered in 1996 and subsequently launched his playwriting career. At the last minute we weren’t able to reserve an actual theater so we had to do the show in a student lounge, using lamps instead of stage lights, dragging props and furniture from the back of my car in the snow. But it turned out that a Lonergan play works well in an extemporaneous space like this, as if the audience just happened upon these people while they were on their way somewhere else.

Lonergan’s always been drawn to smaller, character-driven tales that feel effortless in their calculated naturalism. One of the most successful of these, You Can Count On Me, launched actor Mark Ruffalo’s career and Lonergan’s own as a filmmaker.

But small stories can be tough to mine on a larger scale. Recently, Lonergan was finally able to see the release of Margaret, his long-gestating film starring Anna Paquin that attracted as much attention for its lengthy and controversial rollout as for its subsequent critical praise. He began shooting the film in 2005, though it wasn’t until 2011 that it finally reached an audience. The Village Voice called it “the best movie of the year (that you haven’t been able to see),” and the New York Times referred to it as his “thwarted masterpiece.” Lonergan found himself embroiled in lawsuits and very public rifts with producers in an effort to maintain creative control and release a version he felt comfortable calling his own.

Now, years removed from that experience, he’s able to look ahead to future projects with a bit more ease. Medieval Play, his 2012 broad comedy set in the fourteenth century, was the first in a series of pieces he is producing with New York’s Signature Theatre in the coming years, and he has other film projects on his docket. We spoke in his Greenwich Village apartment, just a block from Washington Square Park,...