Jillian Bell takes the lead in “Brittany Runs a Marathon,” landing her first starring role in the Sundance hit.

“I feel very lucky and the project feels very special, very near and dear to my heart. We’re so proud of what we made,” Bell told Variety at the film’s premiere on Thursday night in Los Angeles. “I feel lucky even when I get to do a small part in anything and to have this be my first title lead role, I couldn’t ask for anything more.”

After stealing scenes in “22 Jump Street,” “Workaholics,” “The Night Before” and “Office Christmas Party,” Bell plays the titular character in the film, a young woman who finds herself prepping to run the New York City Marathon. Writer-director Paul Downs Colaizzo adapted the story from the true-life tale of his best friend, Brittany O’Neill.

“I just felt like I knew who she was. I hadn’t seen her in a movie before and I really desperately wanted to play her. This was the movie that I wanted to see when I was 13 years old,” Bell said.

Her co-stars (including Michaela Watkins and Micah Stock) were similarly moved by the material. Lil Rel Howery (who plays Brittany’s brother-in-law and surrogate father, Demetrius) says the movie inspired him make some big changes in his life.

“This movie made me not be ashamed if I can’t take the first step right away,” Howery said, revealing that he changed his diet and stopped drinking after getting involved in the film. “Anybody that’s looking to take a first step into whatever they want to change in their life, this movie is going to inspire you.”

Utkarsh Ambudkar added that he was encouraged after being cast as Bell’s on-screen love interest, Jern, describing the moment as “triumphant.”

“Being a South Asian in this industry has been challenging,” he said. “Having an opportunity to play the romantic lead for the first time because Paul saw what I might be capable of…it means the world to me. It’s a small little thing…[to play this] silly, charming guy who gets the girl, but I haven’t seen that much from people that look like me on screen. It feels like the 18-mile marker in the marathon. We’re halfway through.”

In some ways, the film’s journey is also at its halfway point. In January, “Brittany” debuted at the Sundance Film Festival to critical acclaim, and Amazon picked up the title in a $14 million deal. However, the real test is still to come at the box office, where indies have struggled this summer.

“You have no idea if people are gonna relate or they’re going to feel like we missed a mark. And I really don’t think we did. Fingers crossed,” Bell said. She explained that hearing early audiences say they can see themselves on screen is “the biggest compliment.”

However, an even bigger compliment came from the “real Brittany,” who posed for photos on the pink carpet with her on-screen avatar.

“[Jillian] got the emotional journey dead on,” O’Neill told Variety, explaining that they didn’t meet until the end of filming. “She needed to identify with the character Paul created and find her own retelling of that. So, when we did meet…it was so nice to connect with her immediately and deeply.”

After introducing the movie’s cast and producers Tobey Maguire, Matthew Plouffe and Margot Hand at the screening, Colaizzo got emotional and reflected on his friendship with O’Neill. “Brittany was fun and joyful, but in moments of candor, she confessed she felt lost. And then one night, because we found ourselves sitting on the floor of the kitchen at 3:00 a.m., she dared to find hope by finding direction. And she did. And I was lucky enough to witness it and be inspired by it and turn my love for her and her newfound courage into a movie. Eight years later, here we are.”

After the lights came up at the screening, the real race began as the studio organized a half-mile walking “marathon” between the theater at Regal Cinemas L.A. Live and the after-party, hosted at Hudson Lofts. After providing flip-flops to attendees who didn’t want to walk in their heels, organizers ushered invitees to the starting line, encouraging them to follow the assigned route marked with enthusiastic volunteers holding motivational signs. Once they reached the finish line, guests, including Blake Anderson, Fortune Feimster. Rachael Leigh Cook, Erin Krakow, Chris Miller and Phil Lord, joined the film’s stars for race-themed cocktails inside the neon-lit event.

“Brittany Runs a Marathon” debuts in theaters Aug. 23.