Ambrose, a longtime smoker, was diagnosed with lung cancer in April. Family members were with him when he died about 4 a.m. at a Bay St. Louis, Miss., hospital, relatives said.
"Steve was the great populist historian of America. He didn't write for intellectuals, he wrote for everyday people," said Douglas Brinkley, a former student of Ambrose's who followed him as director of the University of New Orleans' Eisenhower Center.
Ambrose spent the last six months of his life in a flurry of writing, Brinkley said. His last book, "To America: Personal Reflections of an Historian," which he called his love song to his country, is set for release Nov. 19.
For much of his career, Ambrose was a little known history professor. He burst onto the best-sellers list less than a decade ago with his 1994 book "D-Day June 6, 1944: The Climactic Battle of World War II."
Based in large part on interviews with veterans about their combat experiences, the book recounted the chaotic, bloody beach invasions of Normandy from the American soldier's perspective.
"He was saying, 'There's all this obsession with high command, but the real story is these citizen soldiers who still live in every town and hamlet in the United States,"' Brinkley said.
With unadorned but lively prose, Ambrose continued to captivate readers as he churned out history books at an industrial pace, publishing more than 30, including a half-dozen more best sellers such as "Citizen Soldiers" and "The Wild Blue."
He "combined high standards of scholarship with the capacity to make history come alive for a lay audience," Pulitzer Prize-winning historian Arthur Schlesinger said.
While best known for his World War II books and as the founder of the National D-Day Museum in New Orleans, Ambrose wrote about numerous aspects of American history. Other books addressed former Presidents Eisenhower and Nixon, the Transcontinental Railroad and the Lewis and Clark expeditions of the American West.
"His great gift was that he refused to allow people to think history was boring," said Brinkley, who also collaborated on several books with Ambrose. "He was always grabbing people by their lapels and saying, 'Listen to this. Isn't this fascinating?"'
Ambrose, who called himself a hero worshipper, said in a recent interview that his focus on World War II developed from working on his Eisenhower biography and his memory of GI's returning home from World War II when he was 10 years old.
"I thought the returning veterans were giants who had saved the world from barbarism. I still think so," he said.
For the most part, war veterans were eager to help Ambrose and entrusted artifacts they saved from World War II to the National D-Day Museum. The old soldiers seemed to relate well to the author, a plain-speaking man who got to the point and wasn't afraid to mix in a few curse words for emphasis.
When Ambrose discovered he had lung cancer, he said the likely terminal diagnosis was in some respects liberating because "you can do whatever the hell you want. Who's going to criticize you? And if they do, what the hell do you care?"
By the time he became ill, Ambrose's snowballing success had grown into a dynamic family industry that ranged from top-dollar lectures to movie consulting and even historical tours run by one of his sons.
Ambrose's film work included consulting roles in Steven Spielberg's World War II block buster, "Saving Private Ryan," and on the World War II documentary, "Price for Peace," also directed by Spielberg.
In addition, Spielberg, co-directing with "Private Ryan" star Tom Hanks, turned Ambrose's best-selling book "Band of Brothers" into a cable miniseries.
Ambrose was born Jan. 10, 1936, a doctor's son from Whitewater, Wis. He was for much of his career a ponytail-wearing liberal who once quit a teaching job at Kansas State University in protest over a campus visit from Richard Nixon during the bombings of Laos and Cambodia.
As a young professor, Ambrose counted himself among the growing number of new left professors who taught what was wrong with America, criticizing the treatment of native Americans, U.S. motives for the Mexican-American war and neglect of the environment. But he wasn't always a left-wing academic. He played football for the University of Wisconsin and related his affection for the sport to his fascination with battlefield strategy.
Ambrose spoke out against America's involvement in the Vietnam War, yet he focused his research on presidents and the military at a time when such topics were increasingly regarded by his colleagues as old fashioned and conservative.
Some in academia didn't take Ambrose seriously, which is why, his supporters say, jealousy ran rampant when Ambrose's name became a fixture on best-sellers lists. Some colleagues say that was what led to accusations in early 2002 that Ambrose plagiarized several passages in a handful of books. The passages lacked quotation marks, but were footnoted.
Ambrose apologized for careless editing but otherwise stood by his work.
"I always thought plagiarism meant using other people's words and ideas, pretending they were your own and profiting from it. I do not do that, have never done that and never will," he wrote in a newspaper editorial.
Ambrose seemed to be settling back into a rhythm in the Spring of 2002 when he was diagnosed with cancer. The diagnosis prompted him to drop a World War II project about the Pacific and launch into the autobiographical book due out next month which began with the working title, "A Love Song to America." The book in many ways embodied Ambrose's transformation from left-wing demonstrator to super-patriot.
"I want to tell all the things that are right about America," Ambrose said in a May interview with The Associated Press.
Ambrose, who spent most of his teaching career at the University of New Orleans, founded the D-Day Museum to exhibit artifacts entrusted to him by veterans he had interviewed. It initially was meant for the New Orleans campus but turned into a $30 million exhibit in a converted warehouse.
In an interview earlier this month with The Times-Picayune, Ambrose said he was inspired to continue writing by Ulysses S. Grant, who wrote his memoirs through the pain of throat cancer.
"Dying is so damn complicated," he said.
Ambrose is survived by his wife, Moira, and children Andy, Barry and Hugh, Grace and Stephanie.