William Raymond Manchester was born on April 1, 1922 in Attleboro, Massachusetts. His parents, William Manchester, Sr. and Sallie Elizabeth Rombough Thompson, came from strikingly different backgrounds, both impressing upon young William their family identities. Manchester's father enlisted in the U.S. Marine Corps and served in France during World War I. While fighting in the Argonne Forest he was severely wounded and left for dead. He never fully recovered, dying from complications from these wounds nearly thirty years later. Upon his return home from the war, William, Sr. sought a new profession, his disabled arm having robbed him of his livelihood as a costume jewelry designer. He became a social worker and later a leading advocate in Massachusetts for birth control. In contrast, Manchester's mother was a member of the southern aristocracy. Born in Virginia, Sallie was a descendent of Stonewall Jackson. Their unlikely union was fostered during William, Sr.'s extended stay in the Norfolk hospital where Sallie volunteered. The two married soon after the war and settled in Attleboro.

In 1934, William, Sr. moved his family from Attleboro to Springfield in order to continue his work as a child advocate. Manchester was, by his own account, a sickly child. He spent the better part of his youth harassed by neighborhood bullies. His poor health and general lack of physical strength forced him indoors where he poured over works of literature. Later he sought to overcome his childhood weakness by taking up swimming, a sport in which he excelled. Manchester was a student in the Springfield public school system and entered Massachusetts State College in the fall of 1940. His college career was halted, as many others were, by the outbreak of World War II. Nearly 2,000 men and women from Massachusetts State College enlisted in the armed forces during this time, Manchester among those who volunteered. Honoring his father's legacy, he enlisted with the Marines on July 4, 1942.

Manchester spent his first enlisted year in Amherst, Massachusetts on Inactive Ready Reserve and then moved on to Dartmouth College to participate in the Navy's V-12 program. The V-12 program enabled young men to continue their college education while also providing the Navy and Marine Corps with a ready pool of officers. Some 120,000 men were accepted into the V-12 program and of that number approximately half received a commission. Manchester did not enjoy what he viewed as a mundane existence at Dartmouth and eagerly awaited his orders. During this time, he relied heavily upon letters from family and friends to keep him informed and energized. In particular, his correspondence with his mother and brother, Robert, was a source of joy to him.

His days of drills and classrooms, however, were finally ended in August 1943 when he received orders to report to the Marine Corps Recruit Depot on Parris Island, South Carolina. Notorious for its harsh treatment of young men, the challenges of Parris Island were embraced by the 21-year-old. Even though the physical tests were taxing, Manchester reveled in pushing himself to the limit. Early on the men were told that only a select few would be going on to Officer Candidate School (OCS) at Quantico, the rest would be sent as privates to the base at Camp Lejeune in Jacksonville, North Carolina. Manchester knew that making the cut would be difficult, but his only real moment of concern came when his platoon visited the shooting range. Marksmanship did not come naturally to him, and he worried a poor performance would limit his chances for Quantico. On the day of qualification he registered a score that qualified him as an expert; a score that not only allowed him bragging rights, but also added an extra $10 bonus to his monthly pay.

In spite of his success on the shooting range, Manchester was surprised to receive his orders to report to OCS in November 1943, and even more surprised to learn he was ranked third in his class. Immediately upon arrival, Manchester disliked Quantico. The physical and mental tasks while exhausting were bearable, it was the way in which candidates were dropped that he despised. Officer candidates were subject to peer evaluation, which Manchester feared fostered a vindictive environment. He firmly believed that he was officer material and that the Corps would be making a mistake if they dropped him. Unfortunately, Manchester experienced a set back in his training in February 1944 when he contracted a severe case of scarlet fever. After his recovery, he was forced to fall back a class and watch while members of his OCS class received their commissions ahead of him. Manchester never received his commission and was sent instead to New River.

Assigned to the 29th Marine attachment in Camp Lejeune on May 4, 1944, Manchester was billeted to the eight week Advanced Combat Intelligence Course. He studied enemy weapons and tactics during the course, and spent endless hours on maneuvers in the boondocks. Manchester struck up a brief relationship with a young woman who was a private in the Marines assigned to nearby Cherry Point. He spent his free time with her as well as frequenting the movie theater on base, reading, and swimming on the shore to escape the brutal summer heat. He completed the Intelligence course the second week of July and moved to Tent City, a make-shift camp in another section of Camp Lejeune. Manchester's time in Tent City was short-lived. The Marines received their orders and boarded a troop train on July 8, 1944. The train, scarcely better than a cattle car in Manchester's view, slowly made its way through the scorching summer heat across the southern U.S. to San Diego. While in San Diego, Manchester's mother, who herself had moved to Oklahoma City the previous year, traveled to see her oldest son before his deployment. She arrived on July 26th for a brief visit. Six days later, Manchester boarded a gleaming new transport ship, the , on its maiden voyage to the South Pacific.

Manchester disembarked the nine days later on the island of Guadalcanal. The battle for the island had long since ended, but its beaches and forests were still strewn with remnants of the conflict. Later he transferred to the small Ulithi Atoll in the Western Carolinas. Manchester spent most of his days trying to escape the sweltering equatorial sun and avoiding the dreaded malaria and various types of tropical skin ailments that plagued U.S. soldiers. It was here that the U.S. prepared for assaults on Okinawa and Japan. Ulithi became home to 6,000 servicemen and was a virtual floating warehouse in the South Pacific.

On April 1, 1945 (Manchester's 23rd birthday), the assault was launched to take Japanese airfields on Okinawa. After the previous battles of Saipan, Iwo Jima, and the Philippines in which the Japanese had refused to give up any ground without a rigorous fight, the attack on Okinawa was anticipated to be a bloody and drawn-out battle. The U.S objective to capture Okinawa would cost the lives of 12,000 American soldiers and 107,000 Japanese and Okinawan soldiers. It was by far the bloodiest campaign in the Pacific theater. Manchester and his comrades landed on the beach at 8:27 A.M., but much to their surprise they took the beach and airfields without contest. The Japanese positioned the defense of the island elsewhere and left the initial landing points open. Manchester began making maps and detailing enemy troop movements and fortifications. He was sent out on patrols and watched as men he had trained with died from horrific wounds. The survivors, wracked with stress and grief, were transformed into muddy, bloody messes who often possessed the "thousand-mile stare," a term frequently used to describe combat veterans. Manchester's attachment alone lost 2,812 of the original 3,512 men who landed on the beach. Manchester himself was shot through the kneecap, but left the medical tent when he heard his attachment was on the move. The battlefields became quagmires of mud that would suck down anything less powerful than the Amtrak, and Manchester would later scoff at complaints of mud and rain from men who served in the European theater.

In the opening days of June, the 29th Marines participated in an assault on the Oroku peninsula, located on Okinawa's southern end. On June 4, 1944 during the early hours of the morning, Manchester and his men took shelter in the courtyard of a mausoleum. As they were gearing up for the day ahead, they heard the impending shriek of an incoming round. It was decided that the hillside they were on, in addition to the surrounding courtyard walls, would provide them adequate shelter. They were gravely mistaken. The round landed in the middle of the courtyard instantly killing one man and seriously wounding the rest. Manchester's body was riddled with shrapnel, and he suffered two ruptured eardrums and a severe concussion. Loaded on board a transport ship and sent to Saipan for recovery, Manchester witnessed the war's end from a Navy hospital bed. He later wrote about his experience serving in the South Pacific in .

After the war, Manchester returned to school and received his B.A. from Massachusetts State College in 1946. He next entered graduate school at the University of Missouri where he earned his master's degree the following year. Throughout the 1950s, Manchester worked as a reporter and foreign correspondent for the . With the publication of his first biography, , he turned his attention to fiction, completing four novels in less than ten years. Based upon the strength of his biography , Manchester was hand-picked by the Kennedy family to write the authorized account of JFK's assassination. Despite being selected by the family to write the volume, Manchester's account created controversy even before it was published. The Kennedy family worried that any comments critical of President Johnson and his administration would hurt Robert Kennedy's bid for a U.S. Senate seat. Jacqueline Kennedy also did not approve of Manchester's contract to have the book serialized in magazine. Eventually the manuscript was approved and the account was published in 1968. The book was well-received, even if some reviewers have since described the work as too subjective. With its publication, however, Manchester's reputation as a detailed historical researcher and writer was secured. He followed it up with a biography of Douglas MacArthur and an ambitious multi-volume biography of Winston Churchill, which he was unable to complete before his death.

Manchester married Julia Brown Marshall in 1948 and together they had three children: John Kennerly, Julie Thompson, and Laurie. In 1979, he was hired as an adjunct professor at Wesleyan University, where he taught until his retirement in 1992. Manchester received numerous honors throughout his lifetime, including the National Humanities Medal in 2002. Toward the end of his life Manchester suffered from two strokes. His poor health interfered with the completion of the third volume of his Churchill biography, which he was writing with the assistance of journalist Paul Reid. William Manchester died on June 1, 2004 at the age of eighty-two at his home in Middletown, Connecticut.