Tran Ngoc Chau, a Vietnamese soldier and politician who battled French colonial forces and later the communist Viet Cong, emerging as an influential American ally before being imprisoned in Saigon on treason charges, died June 17 at a hospital in the West Hills section of Los Angeles. He was 96.

His daughter Tamminh Tran Kapuscinska said the cause was complications from covid-19, the disease caused by the novel coronavirus.

Mr. Chau was part of a dwindling group of Vietnamese whose lives were dominated by three decades of conflict, including the resistance against Japanese occupation during World War II, the battle for independence against colonial France and the war that followed the country’s 1954 partition, which pitted the communist North against the U.S.-backed South.

That conflict remained a vivid and sometimes painful memory for Mr. Chau, who spent more than two years at a communist reeducation camp in the 1970s and later fled with his family to the United States, where he wrote a memoir, “Vietnam Labyrinth” (2012), and was featured in the PBS documentary “The Vietnam War” (2017) by Ken Burns and Lynn Novick.

Among American military advisers and intelligence officials, he was perhaps best known as the architect of a novel counterinsurgency strategy that aimed to win hearts and minds in the countryside as the war escalated in the 1960s, and that partly inspired the CIA’s controversial Phoenix program.

While many commanders favored pummeling the enemy with artillery and airstrikes, or employed search-and-destroy tactics to drive the body count upward, Mr. Chau focused on mobilizing rural communities, identifying and resolving the grievances of the country’s peasants and using deadly force only as a last resort.

“We should have been as capable as the Communists,” he wrote in his memoir, “if we, and American leadership, had realized that at heart this war was less about battalions and more about the political cultural feeling of the people in hamlets who were the rural backbone of the nation.”

His approach made him an ally of U.S. operatives such as Edward G. Lansdale and John Paul Vann, the subject of Neil Sheehan’s Pulitzer Prize-winning biography “A Bright Shining Lie.” Introducing Mr. Chau to Daniel Ellsberg, a military analyst who later became an antiwar activist, Vann called him “the most knowledgeable Vietnamese on the subject of defeating communist insurgency I’ve ever met.”

Mr. Chau found success against insurgents in part because he had been one himself. A self-described “son of the mandarin aristocracy,” he had trained to become a Buddhist monk before volunteering as an intelligence courier for the resistance during World War II. He later became a field commander for the Viet Minh, the anti-French coalition formed by Ho Chi Minh, and rose from squad leader to battalion commander.

But he resisted calls to join Ho’s Communist Party — “They didn’t respect our religion or traditions,” he later told Ellsberg — and defected in 1949 to join French-backed forces loyal to Bao Dai, the last emperor of Vietnam. When the French retreated from the region, he served as an army officer in newly created South Vietnam, training local defense forces in the Mekong Delta and rising to become a lieutenant colonel.

Under President Ngo Dinh Diem and his American-backed successors, Mr. Chau served as chief of the troubled Kien Hoa province, mayor of Danang and head of South Vietnam’s counterinsurgency training program. It was there that he aimed to expand the anti-guerrilla efforts he had started in Kien Hoa, a region known as “the cradle of revolution” for its long-standing struggles with communist fighters.

As province chief, Mr. Chau overhauled Kien Hoa’s intelligence operation, creating a “census-grievance program” in which officials were dispatched from village to village, where they conducted one-on-one interviews designed to elicit information about the enemy and complaints about corrupt local officials, who were then disciplined.

With support from the CIA, he also created “counterterror” teams that conducted clandestine missions to capture or kill enemy operatives, with inspectors appointed to investigate allegations of abuse. Official statistics suggested that those efforts were a success, with the estimated number of civilians living in government-controlled areas rising from 80,000 to 220,000 during his first year as province chief.

Mr. Chau’s initiatives “bore more than a passing resemblance” to the Phoenix program, a CIA-coordinated effort that carried out tens of thousands of “capture or kill” operations from 1968 to 1972, according to Dartmouth historian Edward Miller. Critics said that operatives with the program routinely tortured, murdered and assassinated South Vietnamese, accusations that American officials denied.

Mr. Chau later called the program a “perversion” of his original ideas, and he was not directly involved in Phoenix’s creation. Frustrated by infighting within his counterinsurgency program, he turned to politics and was elected to the National Assembly’s lower house in 1967. He rose to become its secretary general, as well as an increasingly outspoken critic of President Nguyen Van Thieu, a former army friend.

Mr. Chau accused Thieu of presiding over corruption in the assembly, and he broke with the president in calling for political negotiations with the North in the wake of the 1968 Tet Offensive. “Tet had convinced him that it was wrong to inflict on the Vietnamese people a war ‘without any end in sight,’ ” Sheehan wrote in “A Bright Shining Lie,” “and he thought that the Saigon side had a chance of surviving if it negotiated a peace in time.”

In an especially risky maneuver, Mr. Chau decided to act as a go-between in unofficial peace talks, meeting in secret with his brother Tran Ngoc Hien, a senior intelligence officer in the North. After the South Vietnamese government found out about the meetings, Mr. Chau was arrested in 1970 for “activities helpful to the Communists.”

Mr. Chau resisted efforts by Vann and others to smuggle him out of the country, deciding that his departure would bolster allegations that he was a Communist Party agent. In a case that made front-page news in the United States, he was sentenced to 10 years in prison at a military trial.

Supporters in South Vietnam and the United States insisted the charges were politically motivated, driven by Mr. Chau’s criticisms of Thieu. And while the South Vietnamese Supreme Court ruled that the trial had been unconstitutional and annulled his sentence, Mr. Chau remained in prison for four years before being released to house arrest.

After North Vietnamese troops marched into Saigon (now Ho Chi Minh City) in 1975, Mr. Chau was put to work at a communist reeducation camp.

“After two years they let us visit him, and we hardly recognized him,” his daughter Kapuscinska said in a phone interview. “We saw an old man, just skin and bones. We had no idea it was him. It was a miracle he survived.”

Mr. Chau was released in 1978 and fled the country with his wife and five children the next year, buying room on a refugee boat carrying members of the country’s ethnic Chinese minority. They made their way to Malaysia and were marooned on an Indonesian island for months before reaching the United States.

Settling in Los Angeles, Mr. Chau studied computing at a community college and took low-paying jobs, working on an assembly line and in the kitchen at a Bob’s Big Boy restaurant before starting a desktop publishing business. For about five years, he and his family pooled their incomes to repay a friend who had lent them the money they needed for their boat trip to the United States — a journey that was paid in sheets of gold bullion costing about $9,000 per person, according to a New York Times report.

“Sixty-three thousand dollars is a cheap price to pay for freedom,” Mr. Chau said.

Tran Ngoc Chau was born in Hue, the former imperial capital, where his father was a judge. His daughter said that few birth records existed at the time, and “just for convenience” his family gave him the birth date Jan. 1, 1924.

Mr. Chau had at least a half-dozen half siblings, all of whom joined the anti-French resistance. When Vietnam split up, most went to the North, while Mr. Chau and two brothers stayed in the South. He entered a military academy and married Ho Thi Bich Nhan.

She survives him, as do seven children; many half siblings; 14 grandchildren; and three great-grandchildren.

While at the military academy in Da Lat, the Chaus befriended Thieu, the future president, and his wife, who together settled in suburban Boston after the fall of Saigon. Despite their falling-out and Mr. Chau’s arrest, the couples resumed their friendship in the 1990s.

“They were best friends again,” Kapuscinska said, adding that their reconciliation was not unusual. “After the fall of Saigon, the North came to the South, brothers met sisters, and people became family again. It was just politics.”

She recalled that while Thieu had initiated the meeting, her father quickly agreed.

“Past is past,” he said.