LOS ANGELES — Connor Jessup, 25, a budding teen heartthrob and a star of the Netflix fantasy series “Locke & Key,” was getting ready for its premiere. But first, he wanted a new nail polish color.

So on a recent Tuesday afternoon, he walked into Helen Nails, a no-frills salon near his boyfriend’s apartment in the Highland Park neighborhood of Los Angeles. He surveyed the rainbow wall of colors and narrowed his choice to an inky midnight blue and fire engine red.

“I spend a lot of my time typing, so I’m just looking at them a lot,” said Mr. Jessup, who clearly isn’t afraid of accessorizing with color. He wore a red-and-blue Eisenhower jacket, faded gray dad jeans and clunky white sneakers. His rumpled brown mop of hair framed his watery green eyes and impish grin.

Another color soon got his attention. “Lovely lavender,” Mr. Jessup said playfully. “The thing that I’m amazed by is that no matter what color you choose, it kind of goes with everything you own, even if it’s, like, just a contrast.”

Mr. Jessup grabbed the lavender and took it to a nail technician, a no-nonsense woman seated at station No. 2. She stripped the chipped cerulean blue from his nails. Then she pushed down his cuticles and clipped the offending skin away. He grimaced slightly as blood gathered near his pinkie nail.

But it would be worth the pain. The next day he would be the center of attention at the Egyptian Theater, where he would walk the red carpet in a roomy green suit alongside his onscreen siblings Emilia Jones and Jackson Robert Scott.

In “Locke & Key,” which is based on the comic books by Joe Hill and illustrated by Gabriel Rodríguez, he plays the brooding Tyler Locke, a teenager who moves into a mysterious mansion where magical keys unlock alternate realities. Family and friends traveled from his native Toronto to cheer him on.

“When I was a kid I was profoundly unsporty and I didn’t have hobbies, but I had energy to burn,” Mr. Jessup said. “I loved fantasy books: Harry Potter and Narnia and ‘His Dark Materials.’ When I was 10 and I had just started acting, this is exactly the kind of job I dreamed about.”

The show could be described as family fare with a fantasy slant, but there are darker themes too. It deftly invokes supernatural elements to address real-world traumas like death and adolescent angst.

“The show is a beautiful, nuanced exploration of what it means to grow up, specifically growing up with trauma or grief,” he said. “Tyler very much can’t deal with what he’s feeling and keeps it all inside. I understand that.”

Mr. Jessup has had his own share of personal growth. Last year, on his 25th birthday, Mr. Jessup took to Instagram to come out as gay. A new relationship and the fact that his birthday fell on the same day as Toronto Pride felt like “a sign from the gay god above,” he said.

“I’m a white, cis man from an upper-middle-class liberal family,” he wrote in the post. “Acceptance was never a question. But still, suspended in all this privilege, I balked. It took me years. It’s ongoing. I’m saying this now because I have conspicuously not said it before. I’ve been out for years in my private life, but never quite publicly.”

Outlets like People and USA Today covered his coming out, and the response was overwhelmingly positive. At that point, he was best known for starring in “American Crime,” an ABC anthology series.

“I’m not dissing anyone, but a lot of people who are doing press for gay projects talk about how, like, it’s a universal story,” Mr. Jessup said, as the technician began painting his nails lavender. “And that’s all true, of course. But, for me, being gay isn’t being straight with a different title. It’s a different experience. Queerness in art, in life, can give you something, you know?”

While he lives in Toronto, where “Locke & Key” was filmed, Mr. Jessup has been spending more time in Los Angeles to be with his boyfriend Miles Heizer, 25, an actor who stars in “13 Reasons Why.” The two met in 2018 when Mr. Jessup acted on an internet crush and messaged Mr. Heizer on Instagram (a few glasses of wine may have been involved). “I guess it could have been worse,” he said. “It could have been Grindr.”

Last weekend, the couple went Instagram official when Mr. Jessup posted a belated Valentine’s Day selfie with Mr. Heizer, with the caption “I’m late but I love you.”

After a second coat of nail polish, Mr. Jessup admired his lavender nails in the afternoon sun. Next he stopped into Kitchen Mouse, a nearby cafe with chalkboards and hanging plants, to fill up on caffeine and chat about his career behind the camera.

He has written, directed and produced several short films including “Boy,” and directed a documentary about the Thai filmmaker Apichatpong Weerasethakul. “As I was starting to act, I also started watching movies and I got really excited about it,” he said. “That went in tandem with learning what acting was. So underneath acting, or I guess inside of acting, was always this desire to make movies.”

Mr. Jessup noticed the sun was setting, and he needed to make his way to Hollywood to greet his mother, who had just flown in. A perk of working for Netflix is that a black S.U.V. was waiting to take him to wherever he needed to go. To say he was excited would be an understatement.

“She’s the kind of person who goes to therapy and after three sessions is giving advice to the therapist,” he said. “She’s my gay icon.”