Vann was born John Paul Tripp in Norfolk, Virginia, out of wedlock, to John Spry and Myrtle Lee Tripp. Vann's mother married Aaron Frank Vann, and Vann took his stepfather's surname; Vann had three half-siblings, from Aaron and Myrtle: Dorothy Lee, Aaron Frank, Jr., and Eugene Wallace. In 1942, Aaron Vann officially adopted him. The Vann children grew up in near-poverty, although, through the patronage of a wealthy member of his church, Vann was able to attend boarding school at Ferrum College. He graduated from its high school in 1941, and from its junior college program in 1943. With the onset of World War II, Vann sought to become an aviator/pilot.
In 1943, at the age of 18, Vann enlisted in the United States Army Air Corps. He underwent pilot training, transferred to navigation school, and was commissioned as a Second Lieutenant in 1945. However, the war ended before he could see action.
When the Air Corps separated from the Army in 1947 to form its own branch, the United States Air Force, Vann chose to remain in the Army and transferred to the infantry. He was assigned to Korea, and then Japan, as a logistics officer. When the Korean War began in June 1950, Vann coordinated the transportation of his 25th Infantry Division to Korea. Vann joined his unit, which was placed on the critical Pusan Perimeter until the amphibious Inchon landing relieved the beleaguered forces.
In late 1950, in the wake of China's entrance into the war and the retreat of allied forces, now-Captain Vann was given his first command, a Ranger company, the Eighth Army Ranger Company. He led the unit on reconnaissance missions behind enemy lines for three months, before a serious illness in one of his children resulted in his transfer back to the United States. While assigned to Rutgers University's ROTC program as an assistant professor of military science and tactics, he received his B.S. degree (with a concentration in economics and statistics) in 1954.
In 1954, Vann joined the 16th Infantry Regiment in Schweinfurt, Germany, becoming the head of the regiment's Heavy Mortar Company. A year later, he was promoted to Major and transferred to Headquarters U.S. Army Europe at Heidelberg, where he returned to logistics work.
Vann returned to the U.S. to attend the Command and General Staff College (a prerequisite for further promotion) in 1957. During this period, he earned an M.B.A. from Syracuse University in 1959 before completing all course requirements for a Ph.D. in public administration at the University's Maxwell School of Citizenship and Public Affairs. He was promoted to Lieutenant Colonel in 1961.
Vann was voluntarily assigned to South Vietnam in 1962 as an adviser to Colonel Huỳnh Văn Cao, commander of the ARVN IV Corps. In the thick of the anti-guerrilla war against the National Front for the Liberation of South Vietnam, Vann became concerned with the way in which the war was being prosecuted, in particular the disastrous Battle of Ap Bac. Directing the battle from a spotter plane overhead, he earned the Distinguished Flying Cross for his bravery in taking enemy fire. He attempted to draw public attention to the problems through press contacts such as New York Times reporter David Halberstam, directing much of his ire towards MACV commander General Paul D. Harkins. Vann completed his Vietnam assignment in March 1963 and left the Army within a few months, having completed 20 years of service.
Vann accepted a job in Denver, Colorado with defense contractor Martin Marietta and succeeded there for nearly two years but missed Vietnam and angled to return. Vann returned to Vietnam in March 1965 as an official of the Agency for International Development (AID).
After an assignment as province senior adviser, Vann was made Deputy for CORDS (Civil Operations and Revolutionary Development Support) in the Third Corps Tactical Zone of Vietnam, which consisted of the twelve provinces north and west of Saigon—the part of South Vietnam most important to the US. CORDS was an integrated group that consisted of USAID, U.S. Information Service, Central Intelligence Agency and State Department along with U.S. Army personnel to provide needed manpower. Among other undertakings, CORDS was responsible for the Phoenix program, which involved "neutralization" of the Viet Cong infrastructure.
Vann served as Deputy for Civil Operations and Rural Development Support CORDS III (i.e., commander of all civilian and military advisers in the Third Corps Tactical Zone) until November 1968 when he was assigned to the same position in IV Corps, which consisted of the provinces south of Saigon in the Mekong Delta.
Vann was highly respected by a large segment of officers and civilians who were involved in the broader political aspects of the war because he favored small units, aggressive patrolling over grandiose, large unit engagements. Unlike many US soldiers, he was respectful toward the ARVN soldiers notwithstanding their low morale and was committed to training and strengthening their morale and commitment. He encouraged his personnel to engage themselves in Vietnamese society as much as possible and he constantly briefed that the Vietnam War must be envisaged as a long war at a lower level of engagement rather than a short war at a big-unit, high level of engagement.
On one of his trips back to the U.S. in December 1967, Vann was asked by Walt Rostow, an advocate of more troops and Johnson administration National Security Advisor, whether the U.S. would be over the worst of the war in six months: "Oh hell no, Mr. Rostow," replied Vann, "I'm a born optimist. I think we can hold out longer than that." Vann's wit and iconoclasm did not endear him to many military and civilian careerists but he was a hero to many young civilian and military officers who understood the limits of conventional warfare in the irregular environment of Vietnam.
After his assignment to IV Corps, Vann was assigned as the senior American advisor in II Corps Military Region in the early 1970s when American involvement in the war was winding down and troops were being withdrawn. For that reason, his new job put him in charge of all United States personnel in his region, where he advised the ARVN (Army of the Republic of Vietnam) commander to the region and became the first American civilian to command U.S. regular troops in combat. His position was the equivalent in responsibilities of a major general in the US Army.
Three days after the Battle of Kontum, Vann was killed when his helicopter crashed into a grove of trees near a village cemetery. He was 47 years old. He was buried on June 16, 1972, in Section 11 of Arlington National Cemetery. His funeral was attended by such notables as Gen. William Westmoreland, Maj. Gen. Edward Lansdale, Lt. Col. Lucien Conein, Senator Edward Kennedy, and Daniel Ellsberg.
In Slow Burn: The Rise and Bitter Fall of American Intelligence in Vietnam, Orrin DeForest cited speculation from South Vietnamese sources that Vann's death was caused by disgruntled South Vietnamese Rangers. "They hated his guts up there," he wrote, and added, "Vann was an abrasive man with a foul mouth, given to embarrassing Vietnamese commanders in public. He'd meet a commander of a unit out in the field some place and he didn't care who was standing around. He'd tell them right there, 'Hey, you dumb son of a bitch, you couldn't run an operation against the VC if you were the last one in the world.' It made no difference to Vann that 'face' was the most significant thing of all to an Asian. You simply cannot embarrass a Vietnamese, at least not in front of someone else. Not unless you are ready to make an enemy for life, one who will get his revenge if he possibly can. He will watch and wait and be patient, and he'll just brood on it until he finds a way to do it."
CORDS Deputy District Senior Advisor Ronald Rockwell worked under Vann for one year while he was the CORDS Deputy at III Corps. Rockwell believes that the quotations describing Vann's behavior toward ARVN commanders are totally unfounded and contrary to everything Vann believed about the proper prosecution of the war.
On June 18, President Richard Nixon posthumously awarded Vann the Presidential Medal of Freedom, the nation's highest civilian citation, for his ten years of service as a top American in South Vietnam. For his actions from April 23–24, 1972, Vann, ineligible for the Medal of Honor as a civilian, was also awarded (posthumously) the Distinguished Service Cross, the only civilian so honored in Vietnam.
Neil Sheehan wrote a Pulitzer Prize-winning Vietnam history and biography of Vann, A Bright Shining Lie: John Paul Vann and America in Vietnam, in which Sheehan also examines two of Vann's alleged career-stunting incidents involving morals charges during his service in West Germany and at Fort Leavenworth, Kansas, and how these possibly affected Vann's future actions and resulting career path both in and after Vietnam. In 1998, HBO made the film A Bright Shining Lie, adapted from the book, with Bill Paxton playing the role of Vann.