Married couple Alex and Tess (Will Arnett and Laura Dern) attend an informal gathering at their friends’ New York apartment early on in the new movie “Is This Thing On?” While the atmosphere is casual and conversational, relations between the pair are frosty, stemming from their prior agreement to separate. 

They intend to tell their friends at the get-together, à la the beginning of Woody Allen’s “Husbands and Wives,” but they hold back, with Tess instead sounding off on youth and the idea of living passionately, though the subtext of her talk is her husband and their marriage. Soon afterward, a chaotic actor friend, Balls (Bradley Cooper), shows up, leading to a funny incident, and the tone is struck for how the rest of the film will balance drama with comedy, particularly when Alex deals with the breakup by doing stand-up comedy. 

Mr. Cooper also helms the movie, and after starring in and directing “A Star Is Born” with Lady Gaga and “Maestro” with Carey Mulligan, he seals his status as not only a sensitive observer of relationships but also as one of the best contemporary male directors of women. While Tess is another in a line of type-A, wryly indomitable characters the actress has played in film and television, the role also allows Ms. Dern to tap into her softer side, with Mr. Cooper helping her to craft one of her most unguarded performances yet. 

For the lead, Mr. Cooper turned not to himself but to Will Arnett, the comedian primarily known for his role in the sitcom “Arrested Development” and from his vocal work in the animated series “BoJack Horseman.” Mr. Arnett developed an initial version of the script with screenwriter Mark Chappell after hearing the real-life story of salesman John Bishop, who took up stand-up after his marriage fell apart. 

An untested dramatic actor, Mr. Arnett nonetheless proves his talent in that regard, with Alex’s depression and confusion over the breakup subtly and convincingly portrayed. Naturally, the actor shines when his character performs at comedy clubs, with the film’s exploration of comedy as therapy another appealing feature. 

Combining two great performances with humor, NYC energy, and a perceptive look at separation, the movie is an adult dramedy and a warm-hearted winner, perfect for the holidays or a date night. 

The film’s key sequence occurs about an hour in, when Tess, who’s unaware of Alex’s moonlighting as a comic, goes one night to the same comedy club in which he will be performing. Mr. Cooper skillfully handles the importance of the individual scenarios in each of their lives, as she is on her first date since separating and he is doing his first real gig.

During dinner before going to the club, Tess, a former Olympic volleyball sensation, discusses returning to the sport via coaching with her date, Laird, who also once played and now coaches. (In a small role, Peyton Manning ably embodies Laird in a nice bit of meta-casting.) Later at the club, she’s confounded when Alex appears onstage, becoming even more so when he jokes in his routine about a recent hook-up while also reminiscing on his former life as a married man. 

The clever way Mr. Cooper melds what each of the protagonists seeks — fulfillment in their professional and personal lives — through this extended sequence demonstrates how the actor-writer-director might one day create a modern-day romantic comedy classic.

With many scenes taking place in the West Village’s Comedy Cellar, one expects some foul language, saucy subjects, and crude gags, with professional jokers like Jordan Jensen, Chloe Radcliffe, and Reggie Conquest also popping up for extra comic cred. Despite this milieu, though, the director’s interest lies more in how a couple navigates separation than in how a middle-aged man finds his way as a comedian. 

A supporting cast that makes up the pair’s friends and family adds further texture and resonance to the themes of domestic uncertainty and personal pursuits, such as when we find out how Balls (Mr. Cooper) and his wife, Christine (Andra Day), are experiencing their own marital issues. Mr. Cooper, in particular, has a lot of fun with the role of a struggling, insecure actor. 

The third act sees Alex and Tess hash out the problems in their marriage in an astounding scene. After a resumption of intimate relations, the two realize that the same issues persist, with the misunderstandings, assumptions, and recriminations fostered in a long relationship bracingly depicted. Tess’s inability to be fulfilled by married life and motherhood is suggested as the ultimate reason for their unhappiness, and though this feels far too definitive for such a complex dynamic, their conversation gets to this conclusion organically and messily, as is the case with most relationship talks.

While a late-stage stand-up scene in which Alex gets super-serious comes off as clichéd and unrealistic — surely someone would have laughed awkwardly or heckled him — it also points to how Mr. Cooper’s sensibilities are fundamentally decent, middlebrow, and sentimental. 

His film contains no huge fights, no sex scenes, and nary an anguish is expressed over the idea of reconciliation or the hard work of changing habits. Just hope, feel-good vibes, and Freddie Mercury singing “Can’t we give ourselves one more chance?” as we exit the theater and head back into our own complicated lives.