By the time Ady Barkan appeared before Congress in May 2019 to advocate for Medicare for All, he had lost the ability to speak. The then 35-year-old lawyer and activist was dying slowly of paralysis from amyotrophic lateral sclerosis (ALS), but as his body weakened, his voice carried. Speaking through a computerized system that converts eye movements along a keyboard to speech, Barkan held the room as he urged lawmakers to dramatically overhaul the US healthcare system.

Even with good private insurance, he explained, he and his family paid $9,000 a month for round-the-clock care. To go on Medicare would relegate him to a nursing home, away from his wife, Rachael King, and their then three-year-old son, Carl. “We are cobbling together the money, from friends and family and supporters all over the country,” he told Congress. “But this is an absurd way to run a healthcare system.”

His testimony forms both the first few minutes and the emotional climax of Not Going Quietly, a new Duplass brothers-produced documentary on Barkan’s improbable route to become one of the leading voices for ethical, accessible healthcare in the US. With unvarnished scenes of caregiving and a heaping dose of Barkan’s sardonic wit, the film, directed by Nicholas Bruckman, traces the central paradox of his life post-diagnosis: the weaker he gets, the louder he becomes.

In the face of declining motor skills, a terminal prognosis (most ALS patients survive three to five years post-diagnosis, though some, such as physicist Stephen Hawking, live decades with the disease), and an eventual tracheotomy, Barkan pleaded a case for universal healthcare fueled by his personal experience. “He used his story as a weapon,” Bruckman told the Guardian, to become, as Politico Magazine called him in a March 2019 profile, “the most powerful activist in America”.

Not Going Quietly observes roughly two years of Barkan and his family’s life as he uses his illness to draw attention to numerous healthcare issues in the US – the exorbitant costs of chronic healthcare, potential cuts to home-health funding, the risk that insurance companies could deny coverage for “pre-existing conditions”. Following his diagnosis at 32 in 2016, Barkan, a lawyer and progressive organizer who had gained limited national attention for focused policy campaigns, took his motorized wheelchair on the road.

In December 2017, he met another organizer, Liz Jaff, while waiting for a flight from Washington DC to Phoenix. Arizona’s Republican senator Jeff Flake happened to be on board. Barkan confronted Flake and urged him to vote against the Trump tax cuts that would probably make healthcare costs balloon. “What should I tell my son, or what should you tell my son, if you pass this bill and I can’t get a ventilator?” he pleaded, while Jaff filmed. “You can be an American hero,” he added. “You could save my life.”

The tactic was unsuccessful – Flake voted for the measure, which passed. But the video went viral, launching Barkan on to the national news circuit and, along with Jaff, a spitballing, indomitable cross-country campaign, Be A Hero, to flip the House in the 2018 midterms on the basis of healthcare reform.

Bruckman connected with Barkan shortly after the Flake incident, in early 2018, to film a brief promo for Be A Hero. Their initial meeting, at Barkan and King’s house in Santa Barbara, California, appears in the film’s first five minutes. Barkan is in good spirits, laughing as King changes his clothes and fluffs his hair. Shirtless, he jokes to the camera: “How about like this?”

“I realized that this is not somebody with even an ounce of self-pity,” Bruckman recalled of that moment. Barkan was “really using humor as a tool to fight back against this disease, in the same way that he was using his story to fight back against what was happening under the Trump administration and the fight that continues to erupt over healthcare in the US”.

By then, Barkan was already more than a year post-diagnosis and had only about six more months left with his natural voice; the pressure was on to record as much of his voice as possible, as Barkan “wanted to create a time capsule of who he was for his son”, said Bruckman.

“We were just all in to capture this chapter in his life,” Bruckman said. Still, Barkan’s declining condition presented Bruckman’s team with several thorny ethical issues – not in how vulnerable to be on screen, or how much of the caregiving process to show (one notable scene depicts Barkan’s best friend, Nate Smith, helping him shower at a campground bathroom on the Be a Hero tour). Rather, the question was how to direct Barkan’s waning reserves of energy. “A lot of days when we were with Ady away from his family, he only had about 30 minutes of voice in him for a whole day before his voice would give out,” said Bruckman. “So we had to decide: do we interview him and have him talk to us about this movie? Or should he call his son for what is one of their limited conversations on the road, and with only a few months left for his son to hear his voice?”

The team frequently chose the latter, opting for a cinema vérité depiction of Barkan’s chats with Carl, eating pasta on FaceTime, or the moments – at a speech, in the RV – when it becomes clear his speaking voice is giving out. The motor decline of ALS is shot through with bracing acceptance and dark humor – at one point, Barkan jokes that the 79-year-old Senator Bernie Sanders “becomes a raisin while I become a vegetable”. At another, he’s stoned in the RV, laughing uncontrollably as he attempts to eat an “ALS-friendly” s’more. Barkan’s final message with his natural voice? “Peace out, motherfuckers.”

“Ady really inherently understood that the nitty gritty, warts and all, the real, authentic, painful, funny, poignant moments of his life were what would make effective advocacy and political change,” Bruckman said. “The goal of these confrontations is not to get Jeff Flake to flip his vote, necessarily,” he said, citing the influence of lobbyists and corporations on lawmakers. “What we can do is we can show the impacts of their policies, we can document that through our stories, we can share that and we can build people-powered movements that win elections,” as in several House districts in 2018, “and gets the politicians replaced.”

Barkan and King, an English professor at the University of California, Santa Barbara, continue to live in California with five-year-old Carl and their daughter Willow, born in 2019. Barkan remains a staunch proponent of Medicare for All and influential progressive voice who prodded all of the Democratic candidates on healthcare before the 2020 election. His endorsement of Joe Biden in July 2020, following the end of Sanders’ and Elizabeth Warren’s campaigns, was a notable win for a Biden campaign eager for progressive figures to actively back the moderate nominee.

Not Going Quietly concludes before all that, before Biden’s victory in the 2020 election and Barkan’s current focus: the fight to pass a $3.5tn infrastructure package with provisions for childcare, healthcare subsidies and eldercare. But the lessons of the Be A Hero tour, and the amplification of one’s personal experience, carry forward. “Ady’s story asks this fundamental question of: well, if Ady can participate in our democracy, what’s my excuse?” said Bruckman.

“What do you do with the time you have left?” he added. “How could something that feels meaningless or painful or tragic or a loss be turned into a tool to make a better world, either for our democracy at large or for the people that you care about in your life?”

• Not Going Quietly is released in US cinemas on 13 August with a UK date to be announced