Jillian Bell is a comedic force who steals scenes with a delivery that slides effortlessly between perky and profane. She’s been an unlikely drug dealer in “22 Jump Street,” a shrewd pimp in “Office Christmas Party,” even an aunt who gets attacked by a vampire poodle in “Goosebumps.” What she’s never played, however, is the lead role.

“A lot of times my character comes in, says something funny and then roots on the leading woman before leaving after talking about her cats or something,” says Bell.

Those days of appearing as the best friend or the quirky neighbor changed with “Brittany Runs a Marathon,” an inspirational comedy about a twentysomething woman who turns her life around when she decides to give up a hard-partying lifestyle and start training. The little indie electrified the Sundance Film Festival, winning the audience award and igniting a bidding war that culminated in Amazon Studios buying the film for a staggering $14 million.

“One of the producers said to me, ‘Don’t ever come back to Sundance. It will never be this good again,’” remembers Bell.

But Sundance is its own beast — an isolated mountain hamlet that embraces things that are offbeat and uncommercial. Now “Brittany Runs a Marathon” faces its biggest test. When it opens in limited release in a handful of theaters on Aug. 23, it will have to slowly build an audience if it wants to break out of art houses and enter the mainstream.

“We think it is really great alternative counterprogramming to all the summer superhero movies,” says Julie Rapaport, Amazon’s co-head of movies, adding, “We don’t expect everyone to show up on opening weekend. It’s about discovery. In many ways there are parallels to a marathon, and we’re in it for the long run.”

Reviews out of Sundance were sterling, and the reaction among crowds, many of whom approached the filmmakers after screenings with tears streaming down their cheeks, demonstrates the picture’s power to move audiences. And yet this summer has been downright hostile to indie fare. “Booksmart,” a sensation at SXSW, and “Late Night,” another comedy that Amazon picked up out of Sundance, may have scored with festivalgoers, but they failed to connect with regular folks when they opened in theaters. Can “Brittany Runs a Marathon,” which arrives without any big-name stars or a well-known director behind it, avoid a similar fate?

“This year it almost feels like nobody has any expectations for anything anymore, so I’m not worried about how it will do,” insists Paul Downs Colaizzo, the film’s writer and director. “I’m curious. I feel like we’ve done all we can do, and now we just hope people will see it.”  

To build awareness, Amazon is deploying the movie’s cast in innovative ways. It’s partnering with Tinder on an initiative that will see Bell and her co-stars team up with the dating app’s users to find matches. The studio has also launched promotional initiatives by pairing up with running apps, health clubs and the San Francisco Marathon. 

“Brittany Runs a Marathon” is something of an anomaly for Amazon. As the theatrical market for indie movies shrinks, the company has begun to experiment with distribution strategies. Upcoming releases such as “The Report,” a political thriller with Adam Driver, and “The Aeronauts,” an adventure film with Eddie Redmayne, will debut in select theaters before appearing a few weeks later on Amazon’s streaming platform. Downs Colaizzo and Bell weren’t interested in that kind of approach. They preferred a traditional theatrical rollout, one that will keep “Brittany Runs a Marathon” on screens for months with a goal of having as many people as possible experience it in a communal atmosphere.

“We want people to leave the comfort of their home and go out and see something together and have conversations about the film afterwards as they walk to their cars in the parking garage,” says Bell. “We want to inspire people to think really hard about what they want to do with their lives.” 

The movie and its message have a personal connection to Downs Colaizzo. Its central character is based on Brittany O’Neill, his best friend and former roommate, who embarked on a fitness odyssey.

“When we were living together, we started having these talks that I’m assuming everyone in their 20s has about the direction of your life,” he says. “We wondered what does being happy look like, and is there such a thing as being happy? A lot of parts of our lives were just dysfunctional. Then one morning she went for a run, and I thought, ‘Oh, this is a movie.’”  

Paul Downs Colaizzo directs Bell on the set of the Amazon film.
Courtesy of Amazon StudiosAnna Kooris

O’Neill says she was flattered that her personal health journey was being reconstituted for the big screen, but when Downs Colaizzo told her the title she had one burning question: “What’s Brittany’s time, and does she finish the marathon in under four hours?” 

In retrospect, it’s easy to see how “Brittany Runs a Marathon” could have veered off track. On paper, the story of a depressed woman in a dead-end job who struggles with body-image issues before finding a sense of self-worth through running might have played as a formulaic crowd-pleaser. Without a deft touch, it might have been one of those romantic comedies filled with makeover montages that falsely implies life would be better and all your problems would go away if only you were a size 6. 

That’s not Brittany’s story, and it’s to the film’s credit that, even as it charts her considerable weight loss, it doesn’t argue that her psychological issues vanish with each trip to the scale. In the film, Brittany is still grappling with the impact that her father’s death when she was young had on her interpersonal relationships. Even as she gets in shape and feels better about her appearance, she’s so self-loathing that she’s wary of taking a chance on a budding relationship with a co-worker (Utkarsh Ambudkar). 

“She worked on the outside, but the inside still needs work,” says Bell. “Sometimes society does something dangerous, which is to look at people who have lost weight and go, ‘Oh, you look so much better.’ Becoming healthier should be celebrated, but taking someone’s weight loss and equating it with beauty is wrong.” 

Bell lobbied Downs Colaizzo for the role, meeting with him at a Brooklyn restaurant and selling him on her vision of how to play the character. But she admits that she worried about what it would take to pull off the performance. Most of the roles she played in the past were broadly comic, but this film required her to have emotional breakdowns and to go to dark places as the character lashes out at the people around her. 

“It was scary,” says Bell. “I was going to have to be very vulnerable in a way I’d never been before, and it was more dramatic than anything I’d ever done. It felt like I was trying on a new hat. I wasn’t sure if the fit would be right or if I’d look ridiculous.”

Then there were the physical challenges. To become Brittany, Bell lost 40 pounds and took up running with the help of a beginners’ workout schedule she found on Pinterest called “The Couch to 5K.” For the movie, she donned prosthetics to play Brittany’s pre-running self. 

To give herself confidence, Bell asked her friend Michaela Watkins to take on the key supporting role of Catherine, Brittany’s neighbor and running partner. “She said she needed me to be there,” remembers Watkins. “It was going to be a lot for her. She was so laid bare on this movie. She was just this open nerve.” 

Downs Colaizzo faced his own hurdles. A playwright with acclaimed Off Broadway shows to his credit, he had never had a screenplay produced as a feature film, let alone directed a movie. But he was concerned that without his involvement his love letter to a friend might be turned into something generic, so he set about convincing the producers and financiers that he could handle the project. He storyboarded scenes and created a book that showed what he wanted the movie to look like. 

“I made a presentation about how this story needed to be told and how I was worried that if it was in the wrong hands it could be told in an insensitive, disrespectful, and ultimately not universal way,” says Downs Colaizzo. “To my great surprise, they said yes.” 

Of course, it helped that “Brittany Runs a Marathon” was shot on a shoestring budget over the course of roughly a month. Many members of the cast worked for scale, committing to the project because they loved the characters and the story. To get the movie wrapped on schedule, Downs Colaizzo worked at a dizzying pace. 

“We were blazing through takes,” says Ambudkar. “I’d think, did you get that? The sound seems weird, and there were trucks everywhere.” 

To supplement his income, Ambudkar got paid to join the likes of Joe Manganiello and Dylan Sprouse for a live game of Dungeons & Dragons in Brooklyn. “I lost money making this movie,” he says. “For me, I just looked at it as an investment based on the script.” 

“Brittany Runs a Marathon” faces a steep climb to box office success, but the filmmakers and cast believe that the response from audiences at Sundance shows that the movie connects on a visceral level, giving it the potential to become a word-of-mouth hit. It would be a shame if people didn’t buy tickets: At a time when Hollywood is being faulted for not providing enough good roles for women, “Brittany Runs a Marathon” dares to offer up one of the most complex protagonists to hit the screens in this or any year. She’s a character who is capable of being funny and thoughtful, as well as caustic and cruel. A woman who struggles to feel good enough and to believe she’s worthy of being loved. And a person who ultimately decides to take matters into her own hands and wrest control of her destiny. If you’re not inspired to lace up your running shoes after seeing this movie, then you should probably just cancel that gym membership. 

“It’s all about going one block at a time,” says Downs Colaizzo. “Change doesn’t happen quickly. You have to change your mindset. You have to unlearn toxic behavior and replace it with victorious behavior. I had a period in my life where I decided that I didn’t want to be the funny sidekick anymore. I wanted to be the lead in my own story.” 

If “Brittany Runs a Marathon” succeeds, maybe there will be more movies where characters who are messy and complicated and rough around the edges don’t just exist on the periphery. They move into the center of the frame.