David Halberstam was one of the first journalists to warn the American public that the Vietnam War was turning into a disaster. In 1964, as the US began its escalation of the conflict, Halberstam was awarded the Pulitzer Prize for his sceptical reporting on the crisis for The New York Times.

His 1972 book, the ironically titled The Best and the Brightest, sought to explain how the vastly talented circle of advisers around presidents Kennedy and Johnson, “ostensibly the ablest group ever to serve in American government”, could have produced “the greatest American tragedy since the Civil War”. His telling anecdotes and painstaking research illustrated dramatically — some said polemically — the imperial arrogance and overconfidence that led these men to ignore or suppress inconvenient evidence, and made the work a bestseller.

Halberstam produced a total of 21 books, on topics as diverse as the car industry, the civil rights movement and the basketball star Michael Jordan. He was killed in a car crash while on his way to an interview for a book he was researching on the 1958 NFL Championship game between the Baltimore Colts and New York Giants, often called “the greatest game ever played”.

But it is the Vietnam War for which he was best known. The defining feature of his work at the time was fearlessness. “There was tremendous pressure,” fellow journalist Neil Sheehan recalled. “David never buckled under it at all. He was capable of standing up to it.”

American generals did not take kindly to his attitude, but Halberstam was not the type to defer to rank. “We do not work for you,” he told one astonished brigadier-general who attempted to dress him down. “We will call a commanding general at home any time we need to get our job done.” In October 1963 President Kennedy is reported to have asked the publisher of The New York Times, Arthur O. Sulzberger, to remove Halberstam from Vietnam on the ground that he was becoming too close to the story. That same month the South Vietnamese police were more direct in their criticism, beating up Halberstam and two other American journalists as they attempted to report on a protest against President Diem.

David Halberstam was born in 1934 in New York, where his father was a surgeon and his mother a teacher. After graduating from Harvard, where he had been managing editor of the student newspaper, he got a job at the Daily Times Leader, a small paper in West Point, Mississippi. He was drawn to the South because of his desire to study the emerging Civil Rights movement. Although he left West Point after a year (apparently he was too liberal for the paper’s editor), he stayed close to the story by moving to The Tennessean in Nashville.

“I couldn’t wait to go to work,” he recalled of that time. “Even though it was often fairly dangerous. I had an intuitive sense that I was watching history . . . something noble.” His coverage of demonstrators and activists confronting an angry establishment inspired his later attitude to reporting. “It made me braver,” he said.

His reports caught the attention of The New York Times, which sent him to Washington and the Congo in 1960 before he was assigned to Vietnam, in September 1962. He returned to New York in 1964. His first book on Vietnam, The Makings of a Quagmire, described the errors of American policy while still arguing that America had a vital interest in winning a just war. By the time it was published, in 1965, he was reporting from Poland. He was expelled later that year after the Communist Government accused him of “slanderous and offensive” reports. He left The New York Times in 1967 to concentrate on writing books, always obsessively researched and usually very long.

Halberstam’s passion and righteous indignation grew from his belief in the centrality of journalism to American democratic life. “He believed it was his duty to change things,” said Horst Fass, a photo-journalist who worked alongside Halberstam in the Congo and Saigon.

This view of the journalist’s task could appear rather portentous to British eyes. One reviewer called Halberstam’s book on the American press, The Powers That Be, a “sentimental, slushy account of not particularly interesting individuals and grossly self-important institutions”.

But Halberstam, in between books on baseball, basketball and rowing, persisted in his self-appointed task of holding power to account. His 2001 work, War in a Time of Peace, was a critique of American foreign policy after the end of the Cold War, and in the light of Vietnam.

In recent years he drew parallels between his experiences in Vietnam and the unfolding debacle in Iraq. “The crueller war gets, the crueller the attacks get on anybody who doesn’t salute or play the game,” he said last year at a conference in Tennessee. “And then one day, the people doing the attacking look around and they’ve used up their credibility.”

He is survived by his wife, Jean, and his daughter.

David Halberstam, journalist and author, was born on April 10, 1934. He died in a road accident on April 23, 2007, aged 73