TAIPEI, Taiwan — Li Zhensheng, a news photographer whose pictures of the blood-drenched Cultural Revolution provided rare and comprehensive visual testimony to the decade-long political turmoil that traumatized Chinese society, died earlier this month in New York City. He was 79.

The cause was a brain hemorrhage, according to his publisher in Hong Kong, the Chinese University of Hong Kong Press, and his longtime photo editor and friend Robert Pledge, the co-founder of the New York photographic agency Contact Press Images. His family did not disclose the exact date of death.

Mr. Li vaulted to international renown in 2003 after Contact Press helped publish his monograph “Red-Color News Soldier,” which contained scores of rare photos from the Cultural Revolution, which lasted from 1966 until leader Mao Zedong’s death in 1976.

The Cultural Revolution, launched by Mao to re-inject proletarian Communist fervor into his flagging national project, sent tens of millions of young zealots onto China’s streets. They staged public show trials, beatings, criticism sessions and “home raids” of bureaucrats and intellectuals. They turned on their teachers, co-workers, friends and parents. The turmoil, which Mao initiated to assert his authority and purge political rivals, is estimated to have caused 1.5 million deaths, many by suicide.

Working during that era as a state newspaper photographer, Mr. Li defied instructions to destroy negatives that contradicted official propaganda. He stored 30,000 negatives under his floorboards, waiting for the right moment to release them.

That moment never came in China. Although the 2003 book, published by New York-based Phaidon Press, has been translated into a half-dozen languages and won an award from the Overseas Press Club in New York, it was barred from print by Chinese censors.

Copies of the Hong Kong version published in 2018 have been confiscated at the border, said Mr. Li, who decried the Beijing government’s efforts to shunt the Cultural Revolution out of public discourse and its history textbooks.

“The Cultural Revolution took place in China, but research into the Cultural Revolution flourishes in other countries and it has little impact on China. I really cannot accept this,” Mr. Li told the South China Morning Post in 2018. “My photos were taken in China and most of my readers should be in mainland China, whether or not they have experienced the Cultural Revolution.

“Many people who have seen the photos would say, could this be possible? How could there be such photos?” he added.

As a photographer for the Heilongjiang Daily in China’s far northeast, Mr. Li captured manic scenes: the Heilongjiang provincial governor forced to have his head shaved publicly and splattered with ink; Red Guards rallying and dancing in sprawling plazas; counter-revolutionaries being lined up to be shot next to a shallow ditch; his own colleagues forcing their leader to wear a dunce hat in a newsroom struggle.

“Were it not for his documentary work, people today would not know about many scenes that took place in those years, or those who remembered who’ve thoroughly forgotten them,” the Wuhan-based writer Fang Fang wrote on social media this week.

Pledge, Mr. Li’s longtime editor, said the photographer was enthusiastic about the Cultural Revolution at the outset and participated in it before growing disillusioned as he witnessed its spiraling destructive force.

“So he began working in this schizophrenic way, both relentlessly recording history, but also serving as a photographer who was part of the state propaganda machine,” Pledge said.

“Almost every major event that shaped our modern world had 10, 15 well-known photographers who documented it,” Pledge added. “In this massive event in China there was only Li, one individual who cut himself into two to witness the dark side of the whole. If he had been born in Paris or New York, he would be 10 times as celebrated as he is.”

Mr. Li was born Sept. 22, 1940, in the port city of Dalian, then under Japanese occupation. He was 3 when his mother died. His father, a peasant farmer, took him to weekly Chinese and Soviet film showings in nearby villages, instilling in him such a love for cinema that Mr. Li would recycle his family’s trash to pay for tickets.

He attended film school, hoping to become a cinematographer, but was reassigned after graduation to become a photographer. He joined the Heilongjiang Daily in 1963 and was sent to the countryside for Maoist reeducation just before the Cultural Revolution exploded nationwide.

As the youngest member of the photo staff, Mr. Li was frequently sent to cover volatile political events. He worked street scenes with a 35mm camera and carefully composed panoramas of mass rallies with his square-format Rolleiflex.

While working, he wore a red armband that identified him as a “Red-Color News Soldier” — revolutionary propaganda worker — which allowed him to shoot darker, more brutal dimensions of the upheaval.

Mr. Li wasn’t immune to political vagaries, he told a London audience in 2012. He worked in constant fear of the newspaper’s political opponents and was betrayed by rivals in 1969. He was sent to a reeducation camp in the countryside, where he served two years’ hard labor along with his wife, Zu Yingxia, an editor at the Heilongjiang Daily.

Mr. Li was able to exhibit his hidden photos inside China once, at a competition in 1988, when the country enjoyed a degree of political freedom under liberal leaders before the bloody crackdown in Tiananmen Square in Beijing one year later.

He met Pledge in 1988 but didn’t begin his book project until 1998, when Mr. Li immigrated to the Flushing neighborhood of Queens, N.Y., and spirited out his massive collection of painstakingly catalogued film. It took the two men three years to cull the negatives.

He and his wife had two children. A complete list of survivors was not immediately available.

In his later years, Mr. Li acknowledged that he had led a revolutionary unit — and struggle sessions — inside the Heilongjiang Daily. That revelation, combined with his role as a state photographer, fueled criticism among some Maoists in China who called Mr. Li an opportunist whose views of the Cultural Revolution shifted according to the country’s political winds.

Mr. Li’s supporters, in response, lamented that he was heckled at a photo festival and on social media — signs, they said, that the Cultural Revolution never really ended.

Pledge said his friend was never an ideologue or fierce Communist Party critic, but that he mostly worried about the suppression of memory.

“The amnesia was his big concern,” Pledge said. “He said: ‘Mistakes were made. Terrible things happened. We have a responsibility to speak about them. We must speak about them.’ ”

CORRECTION: An earlier version of this story incorrectly reported Mr. Li’s age as 80. The story has been revised.