Jurnee Smollett Says She Gained 20 lbs. to Play a Former Marine in Smoke (Exclusive)

Jurnee Smollett is committed to her craft.

Ever since landing her first on-camera gig at just 10 months old, the actress, now 38, has had plenty of experience in transforming into challenging characters. She tells PEOPLE that her latest role in Apple TV’s crime drama series Smoke, opposite Taron Egerton and Greg Kinnear, is no different.

“It’s very instinctual if a character feels like I have to play it, if I feel that there’s certain things in the character that I need to exercise in myself,” she explains. “I was really drawn to this character, Michelle, and when I met [creator] Dennis [Lehane], he said to me something that struck with me and really was my way into her. He said, ‘We all say we want to be happy, and yet we’re drawn to the very things that want to destroy us.’ And that was it.”

Smollett plays Michelle Calderone, a former Marine working as an arson investigator.

She describes Michelle as a well-intentioned individual who “makes a lot of questionable choices” due to the demons of her past despite her goal of “righteousness.”

“It takes a very special person to say, ‘I’m going to put my life on the line, and I’m seeking out danger to fight for this cause that I believe in or fight for justice,’” she admits. “But with Michelle, there’s an added layer of complexity because she’s also a bit single-minded, and because she’s a lone wolf, she doesn’t always follow the rules.”

Fascinated by the depth of the character, Smollett says she did a number of things to prepare, including “severe” workouts.

“She’s someone who uses working out as an escape, and she tries to push herself pretty hard,” she says of her character. “She’s running away from a lot of her emotions and pours it into different aspects of her life working out, but overworking out toxic relationships. She’s a workaholic and very ambitious. So, I knew physically that Michelle needed to have more of a muscular presence than I personally did.”

“I did put on initially 15 pounds, and by the end of shooting, I was up to 20 pounds, because I wanted that part to feel more truthful,” Smollett continues. “She’s a loner. She’s a lone wolf. And so, yeah, she has a little bit of body dysmorphia.”

Michelle also has a lot of trauma from her mother, which Smollett reveals led her to tap into a darker side of her own childhood.

“I had an estranged relationship with my late father growing up,” she shares. “My parents separated when I was really young, when I was 11 or 12 years old, so I could relate to what it’s like to have that parental wound. My mom and I are — it’s the opposite — I’m very close to my mom, so the relationship she has with her mom, I have to kind of fill in the blanks as to how it relates to the relationship I had with my dad.”

In addition to her personal reflection, Smollett says she did research into attachment styles and how trauma impacts people who “don’t do the work to heal that wound.” She also dug into the ways that Michelle’s field of work might affect her, by interviewing marines, firefighters and detectives.

“It was really just about inspecting her choices and asking, well, why is she making such choices?” Smollett notes.

When it comes to keeping her intense work and home life separate, Smollett, a mom to 8-year-old son Hunter, says she has several rituals.

“There’s something about water that’s always so calming for me, baths or cold showers or things like that,” she reveals. “Water has always been a way for me to be able to transition and physically wash the character off of me. I also have a son, and so my process over the years, it’s just changed. I’ve had to become more efficient with my process and I don’t really have the luxury of staying in it too much.”

“Also, I really think of the work, it’s your instrument,” she adds. “You either tune it up or you tune it down. You modulate it based on the need, based on the schedule. If you’re doing a scene, and you know you gotta come back the next day, you kind of modulate it so that the residue of it stays with you and that you just learn to develop a level of stamina.”

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Smoke is now streaming on Apple TV+ with new episodes dropping weekly on Fridays.