Perhaps my favorite supporting player in the movies over the last few years is Steppenwolf’s own Tracy Letts.

From “The Big Short” to “Wiener-Dog,” from “Indignation” to “Christine” to “Elvis & Nixon,” Letts has been a commanding presence every time he’s featured in a scene. He can be simply standing still, fixing a gaze on someone else in the room and listening intently, and it is still interesting and unique work.

Letts steps into a lead role in a dark, emotionally bruising and brutally insightful work called “The Lovers” — and he is spectacularly good.

The same could be said of the other main performers in a film that often comes across as a (brilliant) piece of theater: Debra Winger, Aidan Gillen and Melora Walters.

Letts plays Michael, a middle-aged man about 25 years deep into a lifeless and seemingly loveless marriage to Debra Winger’s Mary. They both have mundane, cubicle-bound office jobs where they appear to be closer to getting fired than moving up the corporate ladder.

Once they’re both back at home — a comfortable but dimly lit house that gives off a depressing, empty-nester, playing-out-the-string vibe — they retreat to their separate spaces, barely saying a word beyond bare-bones exchanges about their upcoming schedules.

Mary might pour a goblet of wine and escape into a movie playing on TV, while Michael is often so exhausted and beaten down by his workday, all he wants to do is climb into bed. Before turning out the lights, they politely say goodnight to one another, and that’s that. We get the feeling they haven’t had sex since the early days of the Obama administration.

Not that Michael and Mary are leading excitement-free lives. Michael is in the throes of a heated affair with a free-spirited, bundle-of-nerves dance instructor named Lucy (Melora Walters), while Mary is carrying on with a writer named Robert (Aidan Gillen).

Neither knows about the other’s shenanigans. (Little wonder, given they’re both so self-absorbed and so utterly uninterested in their marriage.)

Writer-director Azazel Jacobs has a keen ear for the way people in long-term affairs often lie to one another as much as they lie to their spouses. (Inevitably the post-coital conversations turn to whether or not the affair is actually going anywhere.) He has an equally deft touch for the dynamics of the workplace, and the oft-joyless grind of it all.

RELATED: Tracy Letts says ‘Lovers’ lead role came ‘out of left field’

Just before Michael and Mary are to host their college student son Joel (Tyler Ross) and his girlfriend Erin (Jessica Sula), something unexpected and strange and inexplicable and farcical transpires between them, throwing their lives into yet another level of chaos. Meanwhile, the impulsive Robert and the clinging Lucy are both on the verge of either breaking things off or going public with their respective affairs.

Joel shows up with a 10-pound chip on his shoulder, spoiling for a confrontation with his parents, whom he says have hated each other forever. He keeps on telling Erin he’s nothing like them and he wishes they would just get divorced and stop tormenting each other and him — but what Joel doesn’t see is he’s actually JUST like his parents on a number of levels. The poor kid is in need of about a dozen years of intense therapy and anger management counseling, and he doesn’t even know it yet.

“The Lovers” gets a tad too theatrical in the last act, and the deeply cynical resolution might not sit well with everyone. (I thought it was just about perfect.)

But just about every step of the way, the dialogue crackles and the performances are electric.

★★★1⁄2

A24 presents a film written and directed by Azazel Jacobs. Rated R (for sexuality and language.). Running time: 94 minutes. Opens Friday at local theaters.