Colin Powell was born in the New York City neighborhood of Harlem in 1937, and raised in Hunts Point, South Bronx. His parents, Luther Theophilus Powell and Maud Ariel (née McKoy),emigrated from Jamaica to the United States and worked in Manhattan's Garment District. Colin Powell is also of Irish ancestry.

Powell was educated at Morris High School, a former public school in The Bronx, New York City, from which he graduated in 1954. He gained a bachelor's degree in geology from City College of New York attaining a "C" average, according to his 2006 graduation address at Marymount University. He later obtained an MBA from The George Washington University after his second tour in Vietnam in 1971.

While at City College Powell joined the Reserve Officers' Training Corps and later described it as one of the happiest experiences of his life: finding something he loved and could do well, he had "found himself." Cadet Powell joined the Pershing Rifles, the ROTC fraternal organization and drill team started by GEN John Pershing. Even after Powell became a General, he still kept on his desk a pen set he had won for a drill team competition. After graduating from City College in June 1958, he was granted a commission as an Army Second Lieutenant. Powell was a professional soldier for 35 years, during which time he held a variety of command and staff positions and rose to the rank of General. Powell obtained an MBA from George Washington University in 1971 and then served a White House fellowship under President Richard Nixon. In his autobiography My American Journey, Powell mentioned several officers he served under that inspired and mentored him.

As a Lieutenant Colonel serving in South Korea, for example, Powell was very close to General Henry "Gunfighter" Emerson. Powell said he regarded this man as one of the most caring officers he ever served under. Emerson reputedly had a somewhat eccentric personality. For example, he insisted his troops train only at night and made them repeatedly watch the television film Brian's Song to promote racial harmony. Powell always professed, however, that what set Emerson apart was his great love of his soldiers and concern for their welfare.

While serving with the Third Armored Division in Germany as a Lieutenant, he met Elvis Presley, then serving in that unit. During the Vietnam War, Powell served as an advisor from 1962 to 1963. He returned to Vietnam from 1968 to 1969 where he served as the executive officer and later as the assistant chief of staff of operations for the Americal Division (the 23rd Infantry Division) with the rank of Major, was charged with investigating a detailed letter by Tom Glen (a soldier from the 11th Light Infantry Brigade), which backed up rumored allegations of the My Lai Massacre. Powell wrote: "In direct refutation of this portrayal is the fact that relations between American soldiers and the Vietnamese people are excellent." Later, Powell's assessment would be described as whitewashing the news of the massacre, and questions would continue to remain undisclosed to the public. On May 4, 2004, United States Secretary of State Colin L. Powell said to Larry King, "I mean, I was in a unit that was responsible for My Lai. I got there after My Lai happened. So, in war, these sorts of horrible things happen every now and again, but they are still to be deplored."

In the early 1980s, Powell served at Fort Carson, Colorado. It was there that he had a major clash with General John Hudachek, his commander. Hudachek said in an efficiency evaluation that Powell was a poor leader who should not be promoted. Many of Powell's supporters have said this was pettiness and spite on Hudachek's part and Powell's rising military career was unhindered by Hudachek's evaluation report. After he left Fort Carson, Powell became senior military assistant to Secretary of Defense Caspar Weinberger, whom he assisted during the invasion of Grenada and the raid on Libya. In 1989, prior to being named Chairman of the Joint Chiefs of Staff, Powell served as the Commander in Chief, Forces Command headquartered at Fort McPherson, Georgia.

At the age of 49, Powell became Ronald Reagan's National Security Advisor, serving from 1987 to 1989. He retained his Army commission (he was a Lieutenant General at the time of his nomination) while serving as National Security Advisor. After his tenure with the NSC, Powell was promoted to 4-star General under President George H.W. Bush and served as Commander-in-Chief (CINC) of the United States Army's Forces Command (FORSCOM), overseeing all Army, Army Reserve, and National Guard units in the Continental U.S., Alaska, Hawaii, and Puerto Rico.

His last military assignment, from October 1, 1989 to September 30, 1993, was as the 12th Chairman of the Joint Chiefs of Staff, the highest military position in the Department of Defense. At age 52, he became the youngest officer to serve in this position. In 1989, he joined Dwight D. Eisenhower and Alexander Haig as the third general since World War II to reach four-star rank without ever being a divisional commander. During this time, he oversaw 28 crises, including the invasion of Panama in 1989 to remove General Manuel Noriega from power in the United States invasion of Panama and Operation Desert Storm in the 1991 Persian Gulf War. During these events, Powell earned his nickname, "the reluctant warrior". He rarely advocated military intervention as the first solution to an international dispute, and instead usually prescribed diplomacy and containment.

Powell mentioned in his autobiography that he is haunted by the nightmare of the Vietnam War. He felt the leadership was very ineffective. Powell served a tour in Vietnam as a military advisor, and was badly injured when he stepped on a bamboo "punji stick." The massive infection nearly killed him and it shortened his first tour. It was also during his Vietnam service, his second tour, that Powell was decorated for bravery. He single-handedly rescued several men from a burning helicopter, one of them being Maj. Gen. Charles Gettys, the commander of the Americal Division.

Powell opposed to the majority of George H.W. Bush Administration officials who advocated the deployment of troops to the Middle East to force Iraqi leader Saddam Hussein to withdraw his armies from neighboring Kuwait, believing the dictator could instead be contained through sanctions and a buildup of forces around Kuwait.

As an officer, Powell also valued loyalty very highly, and as a result, did not usually "undermine force" to achieve a military objective while minimizing U.S. casualties. These sentiments have become central tenets of what has since been dubbed the "Powell Doctrine".