Thousands of people had gathered amid the red dirt and golden grass of an Australian Outback cattle town to commemorate a watershed moment for Indigenous rights. Thomas Mayo was there to make a push for the future.

A tall, strongly built man wearing a maritime labor union T-shirt and an amulet shaped like an Indigenous woman’s headdress, he started the day looking like what he was: A proud Australian dock worker whose family roots preceded British settlement.

When local elders asked him to speak, he had every reason to open with grievance or fury. Indigenous Australians — the first inhabitants of the continent who now account for barely 4 percent of its population — remain severely disadvantaged as a group, with shorter life spans and more extreme poverty.

Instead, Mr. Mayo introduced himself quietly, with his eyes down. Then he recited from memory what his fellow Indigenous leaders called a “statement from the heart.” They were requesting a constitutional amendment that would create a panel to advise Parliament on Indigenous issues. They called it the Voice.

Mr. Mayo spoke up for it in conversations and speeches from dawn to nightfall, with a tone that was thoughtful and inviting, hopeful not angry.

“Naysayers have told us to lower our sights and dampen our aspirations for change because of some lazy speculation that the Australian people won’t support real change for our mob,” he said to the crowd, as the sun was setting that day last year. “I believe this is a miserable caricature of the Australian people. We cannot allow this low-bar politics to hold us back.”

Over the next 14 months, he explained the Voice to groups small and large. At times, he seemed to be everywhere, on the radio, in newspapers (including this one), at rural gatherings and knocking on doors in suburbs. Along the way, he told me he was optimistic about the referendum because “there’s just a lot of logic in it.”

He trusted Australians to recognize the modesty of the Voice, which resembled what already exists in Canada and Scandinavia.

More than anything, he trusted people to listen and vote for what most Indigenous Australians said they needed.

But there was opposition even within the Indigenous community. One Aboriginal leader in Parliament criticized the Voice as toothless. Another said it was too divisive. What Mr. Mayo saw as a proposal of respect was perceived as vague by many Australians, in particular conservative politicians, helping misinformation and lies, including false claims about an Aboriginal land grab, gain traction on social media. Opponents leveraged the confusion — “if you don’t know, vote no” was a popular slogan. And on Oct. 14, with voting mandatory, as always in this country, Australians resoundingly rejected the Voice referendum.

Several weeks later, Mr. Mayo would explore what he learned from defeat. On Election Day, at a polling station, he just looked tired. Heavy bags ran like shadows under his eyes; his hair, usually tightly shaved, had grown out enough to reveal spots of salty gray.

“I love his calmness,” said Norma Ingram, a Wiradjuri elder who has known him for years, watching him speak to reporters. But, she added, the campaign’s impact would linger. The Voice was meant to be a first step, a pivot toward greater inclusion. Even for him, it would be hard to go on.

“It’s brought out the worst in people,” Ms. Ingram said. “It’s been horrible.”

A Darwin Upbringing

Mr. Mayo’s parents met in a mining town called Frances Creek in the Northern Territory. His father was a Kaurareg Aboriginal and Kalkalgal, Erubamle Torres Strait Islander man; his mother was the daughter of Polish refugees. Their family, with Thomas and his two younger sisters, later settled in Darwin.

After high school, Mr. Mayo started working at the wharf, where in the late 1990s the port’s owner tried to bust the union. Australia’s labor movement fought back, and Mr. Mayo faced his first leadership test.

“I was 21,” he said. “The company brought on all these guys twice my age who thought the boss was a good bloke.”

“Just teaching these guys to stick together,” he added. “It was really hard.”

He worked up the union ranks and built a family. A father of five, he only started to think more deeply about Aboriginal issues in 2014, when funding for Indigenous programs was slashed. Protests broke out but little changed, leading Mr. Mayo to get involved in a movement to draft a constitutional referendum that would help empower Indigenous Australians.

In 2017, Mr. Mayo was among 250 delegates who finalized the Uluru Statement from the Heart, calling for a reconciliation program that would start with the Voice and, they hoped, eventually lead to a treaty and truth commission.

To build support, Mr. Mayo took the original document on the road. A mix of Aboriginal art and text, the signed canvas was the size of a carpet. He rolled it out on the sand in remote communities and on the floors of city offices. For 18 months, he crisscrossed Australia, sharing the document and reciting its words in the steady voice that became his signature.

The Maritime Union of Australia kept paying him as he campaigned full time. His colleagues were proud to see his higher profile, and the Voice was gaining momentum. In 2022, a new Labor prime minister, Anthony Albanese, promised to put it out for a vote. A few months later, Mr. Mayo published a book, “Finding the Heart of the Nation,” about the Uluru journey, and it became a best seller.

Early polls looked promising, but opposition grew steadily.

Mr. Mayo stuck to the script. Meeting university students one rainy morning, he encouraged them to ignore the noise and extremes. “We’re going to win this with the large middle of Australia,” he said.

Then the middle started to turn. Cab drivers told Mr. Mayo they’d heard that the Voice would stop Parliament in its tracks, and as he tried to combat that misinformation — legal scholars confirmed that the Voice would simply inform decision-making, not halt legislation — he found that social media drowned out his voice. Ugliness took over. He was accused of being a communist. Memes with images of his parents tried to cast doubt on his Indigenous roots. He was attacked with a racist cartoon in a major newspaper, and faced death threats.

“Being a wharfie from a strong blue-collar union, a big black man, a rugby league player — they were hoping I’d get angry,” he said.

He never lashed out. A voice for the Voice, he tried to stay kind.

“He has been a leader who has shown extraordinary dignity and compassion,” said Tanya Plibersek, Australia’s environment minister. “He’s really focused on the issues, the cry for justice. He’s convinced so many people because of that.”

The Aftermath

By the time the votes were counted, Mr. Mayo had been promoted by the union and had fielded calls to run for Parliament. He returned home for silence and reflection — a planned respite organized by Indigenous leaders. Some were so dejected they considered pulling back from public life permanently. Others called for a new, more confrontational approach.

Mr. Mayo ended up somewhere between despair and explosive outrage, with a more nuanced view of anger and mobilization. At home in Darwin, flanked by a bookcase with novels by Salman Rushdie and Joseph Heller’s “Catch-22,” he said he hoped to write a guide of some kind with lessons for young people from the past few years.

His main conclusion: “People must get political. What I mean is, they need to challenge their friends and their family and the sources of their information.”

Noting that the “yes” campaign mobilized 70,000 volunteers, he said informing and deploying more people was the only way to proceed. Instead of condemning social media, he called for people to master difficult conversations and work with institutions — like unions — that have real-world expertise.

“We’ve got to adapt quickly,” he said.

“I don’t say to young people, ‘don’t be angry,’” he added. “But what I do say is that we need to coordinate, we need to have realistic goals and not just anger for anger’s sake.”

So instead of being furious with the Australian people for rejecting the Voice, he said, “I’d prefer that any anger that I have be for those that lied to the Australian public.”

His voice rose — just a little.

“What we tried to do will be achieved one day,” he said, wiping sweat from his brow. “It might not be for decades, but it will be — we’ve just got to do the work to make that happen.”