The sense that actors Adam Driver and Scarlett Johansson are having their best year ever is cemented by their moving yet understated work in Marriage Story, writer-director Noah Baumbach’s most polished and heartfelt film to date. Johansson and Driver are Nicole and Charlie, a young couple with an 8-year-old boy who are, respectively, the star and artistic director, of an avant garde New York City theater company. The movie begins with two sweet montages as the characters narrate what they like most about their spouse — but the paired essays turn out to be exercises in a fraught marriage-counseling session.

It’s all downhill from there.

Divorce is a common theme in Baumbach’s films — his first to garner significant critical acclaim was The Squid and the Whale, told from the children’s point of view. But Marriage Story doesn’t side with either Charlie or Nicole, as Baumbach portrays each with both sympathy and critical distance.

Although the crux of the escalating dispute is custody of Henry (Azhy Robertson, Juliet, Naked), this is no Kramer vs. Kramer with a clear villain. It’s a messy, no-good-answers slice of life that traces how two people who hoped to split amicably and without lawyers in New York wind up in court in Los Angeles, represented by vicious attorneys. Laura Dern, breezily magnifying her Big Little Lies role as a rich creep, takes Nicole’s case, while Charlie consults with the nasty, expensive Jay (Ray Liotta) and the well-meaning but schlubby Bert (a perfectly cast Alan Alda).

Also notable in the supporting cast are Julie Hagerty as Nicole’s hyperactive mom, Merritt Wever as her often-nervous sister, and Wallace Shawn as an egocentric member of Charlie’s theater company. The theater subplot — avant garde goes to Broadway! Charlie wins a Guggenheim! — is a bit creaky, and we have to assume Baumbach is making fun of overhyped avant garde shows in general, perhaps as contrast to the hyperreality in the lives of its participants. Surely we can’t be mean to take seriously the silly fragments of a pretentious play we see.

But the career context provides an important theme: Among Baumbach’s achievements here is the gradual revelation of Charlie’s and Nicole’s very different perspectives on what seemed for years a loving marriage and productive artistic partnership, and the ways in which small infractions or disagreements can become heinous accusations in a legal tussle.

Driver and Johansson are wonderful throughout — not because they’re flashy and melodramatic but because they stay vulnerable and even chummy while their distance and distrust builds. A key scene in which their differences escalate cements both actors’ performances as among the most human and carefully modulated of the year.

This is heavy stuff, yet Baumbach also sprinkles in realistic humor and moments of affection that keep the movie and the characters warm and genuine. As always, his filmmaking is low-key, meant to capture his cast at their best and to underline their relationships — whether divided or intertwined — with subtle visual cues and a minimum of directorial flash. The final scenes are bittersweet and touching with a subtlety rare in the age of This Is Us.

This is a film that showcases the complexities of people and feelings above all else, and one that viewers may feel and remember for years to come.

Grade: A. Rated R. Opens Friday at Grail Moviehouse.

(Photo: Wilson Webb/courtesy of Netflix)