On a recent Tuesday morning, Parker Posey met me outside her Chelsea apartment building, wearing a billowy black Rachel Comey skirt, a vintage navy poplin blouse, and nothing on her feet. “Hello-o-o!” she cried, waving wildly at me from across the street. When I got closer, she coquettishly batted her eyes, which were painted with iridescent eyeshadow. “I put it on for you,” she said. She led me up a narrow set of stairs, past walls painted with psychedelic stripes that she told me were inspired by the work of the avant-garde color theorist William Tapley. Inside her apartment, the groovy vibe remained. In the living room, next to a built-in banquette and a huge arched window sat a working fireplace made out of adobe-style bricks, lending the room the feel of a Laurel Canyon bungalow. Posey, who is fifty-three, moved into the place four years ago, after moving out of a West Village home that she’d shared with a friend’s elderly mother. But she hasn’t spent much time there because she’s been busy caring for her aging mother in Mississippi and performing in several projects, including “The Staircase,” a dramatic new HBO Max miniseries from the filmmaker Antonio Campos that revisits a grisly 2001 murder case.

In the nearly three decades since her first starring role, in the 1995 indie comedy “Party Girl,” a “Parker Posey” character has become almost its own acting genre. Her quirky performances—spiky, daffy, ruthless, silly to the extreme—make even her tiny parts marvellously memorable: the queen bee-bitch yelling “Air raid!” in “Dazed and Confused,” the chain-smoking purveyor of the “Ding that, Skippy!” monologue in “Kicking and Screaming,” the entitled, over-caffeinated book editor in “You’ve Got Mail.” And of course her many roles in Christopher Guest’s œuvre, where she stands out even amid a murderers’ row of comedic talent. I have rarely laughed as hard as I did the first time I watched Posey’s character audition in “Waiting for Guffman,” throwing herself flirtatiously at a local gay theatre director while singing Doris Day’s “Teacher’s Pet.” Her lines from “Best in Show,” most of which she improvised on set (“Why didn’t you tell me that before? Thanks for your help, you stupid hotel manager!”), have become cult canon. In “The Staircase,” which was based in part on a docuseries of the same name, Posey plays the late Freda Black, the assistant district attorney in the murder trial of Michael Peterson (Colin Firth), a wealthy North Carolina writer whose wife, Kathleen (Toni Collette), was found dead at the bottom of their mansion stairs. Black distinguished herself in the courtroom with clownish eye makeup and pearl-clutching appeals to the jury, but Posey told me that she saw more in the character than campy antics. For one thing, Parker had never before played a fellow Southern woman.

After we spoke for an hour or so at her apartment, Posey announced that she needed to go to the Soho Rachel Comey store to pick up a sparkly outfit to wear to the première of “The Staircase,” at MOMA that evening. She put on lace-up oxford shoes, oversized plastic glasses, and an N95 mask on a pearl chain that she fashioned herself out of an antique necklace. On the street, I quickly discovered that Posey loves to talk to strangers. She stopped to coo loudly at several dogs. When we passed a row of movie trailers set up for the filming of another TV show, “Fleishman Is in Trouble,” Posey rapped on the door of one. “When am I needed on set?” she asked in an impatient tone, fully confusing the assistant inside. When she passed a man sitting in an idling delivery truck, she walked up to his open window and asked if he ever takes a nap while resting his head on a roll of paper towels (“I just know Teamsters,” she said afterward.) In Washington Square Park, she ran into her old friend, the actor Justin Theroux, out walking his rescue pitbull. They kibbitzed about current projects and made plans to get together soon. As we walked away, Posey told me that she and Theroux wanted to remake the nineteen-eighties series “Hart to Hart,” which starred Robert Wagner and Stefanie Powers as a married couple who solve crimes. The twist, she said, was that they wanted to use the same scripts as the original show, without changing a word. It’s a kooky idea, but would you expect anything less?

This conversation has been edited and condensed.

You just got back in town.

This weekend I was working on a movie called “The Parenting.”

This is the one with Brian Cox?

Gosh, how do you know? Are you a psychic?

I have IMDb.

I’ve played a lot of dark ladies in the past year or so. Dr. Smith in “Lost in Space,” a stint in “Tales of the Walking Dead,” Freda Black, and then a part in Ari Aster’s new movie, “Disappointment Blvd.” “The Parenting” is a horror comedy about parenting, and I play a wacky-neighbor part.

Not a stretch.

Not a stretch at all. She has an Airbnb, and a gay couple come to introduce their parents in this house. It was fun. I kind of play a witch. I have one more day of shooting in a few weeks. We had our poster shoot on Sunday, which you wouldn’t think would be tiring, but I was jumping around and running around, lots of output, lots of jumping up and down.

It is tiring getting your photo taken!

You want to see it?

The jumping?

Yes! You want to see it? [Stands up and leaps in the air.] It’s like that.

That’s a lot of cardio. Let’s talk about “The Staircase.”

I love Antonio [Campos]. I met him in 2008 with “Broken English.” That was at the Deauville Film Festival. He was, like, “I have this movie, ‘Afterschool,’ that’s screening here. I’d love for you to see it in New York.” I’m, like, “I would love to—oh, my God, this is so cool.” Like, a younger-generation filmmaker reaching out to me and reminding me of the nineties, when that happened all the time. I saw it uptown somewhere and thought, Wow, this is the real deal. He’s got such style and vision and a way of telling a story that’s very eerie, very Americana. I don’t know if that’s the right word, but there’s a darkness. There’s humor, but it’s really subtle.

I want to get to your role as Freda Black, but first can we discuss Colin Firth’s voice? It’s so spot-on, it’s scary.

Well, we all freaked out at the Zoom readings. I just got creeped out because he was so uncanny. He just really stepped it up. Wow. He’s worked on this with my old teacher from SUNY Purchase who I loved, Elizabeth Himelstein. She is a speech teacher, a dialect coach. She once gave me a pair of her Norma Kamali high-heeled tennis shoes. Have you ever seen those?

I mean, sure.

Liz was a really important teacher for me at Purchase. There are a lot of full circles happening now, which I love. I moved to New York in 1992, and my first apartment was in Chelsea, just down the street from here. I mean, life is stressful and overwhelming and there’s anxiety. But I do see that there are circles being closed. Do you know what I mean? I know that sounds hippy-dippy.

At a certain point in your life, you start to see things holistically. So was she always a dialect coach—this teacher of yours, Liz?

Yeah. I’d call her a speech coach. I actually made a recording for her down South, when I went to see my parents, of all these different Southern accents that she still uses.

So you already had Freda’s Southern accent in you somewhere.

I got really just immersed in playing her. With Freda, there’s a lot of interviews to watch. And I read this book, “Written in Blood.”

It sounds like a very salacious read.

It is a very fast read and is geared toward the prosecution’s case. I actually fell asleep reading it, and I ended up talking to Antonio about how maybe we can get windchimes, like how they did at the grave of Kathleen. And he was, like, “What?” I guess I had made that up as I was falling asleep reading. I didn’t have a nightmare, but I did have these fantasies that were, like, hallucinations.

How did you get into the documentary to begin with? Were you obsessed with it when it came out?

Weren’t you? I mean, I think I watched it a few times even back then. I love documentaries. The Frederick Wiseman documentaries, Albert Maysles. You see how subjective they are, too.

The Juliette Binoche character. I won’t give it away, but what she does is so unethical.

People are going to scream. They’re going to die.

Did you all talk among yourselves about whether Michael Peterson is guilty?