John Chapman was born on July 14, 1965, in Springfield, Massachusetts, and grew up in Windsor Locks, Connecticut. He enlisted in the U.S. Air Force on September 27, 1985, and was trained as an Information Systems Operator. Chapman's first assignment was with the 1987th Information Systems Squadron at Lowry AFB, Colorado, where he served from February 1986 to June 1989. He then cross-trained into the Combat Control career field and served with the 1721st Combat Control Squadron at Pope AFB, North Carolina, from August 1990 to November 1992. His next assignment was as a Special Tactics Team Member with the 320th Special Tactics Squadron at Kadena AB, Okinawa, from November 1992 to October 1995. Sgt Chapman's final assignment was with the 24th Special Tactics Squadron at Pope AFB, where he served from October 1995 until he was killed in action in the opening days of the War on Terrorism in Afghanistan, on March 4, 2002. He was buried at the St. Mary Byzantine Cemetery in Windber, Pennsylvania. John married Valerie Novak of Windber, Pennsylvania, on August 22, 1992, and they had two children together, Madison and Brianna. On April 8, 2005, the container ship MV Merlin (T-AK 323) was renamed the MV TSgt John A. Chapman in his honor. TSgt Chapman was originally awarded the Air Force Cross for his heroism the day he was killed in action, but it was later upgraded to the Medal of Honor on August 22, 2018. He was posthumously promoted to Master Sergeant the next day, on August 23, 2018.

His Medal of Honor Citation reads:

Technical Sergeant John A. Chapman distinguished himself by extraordinary heroism as an Air Force Special Tactics combat controller, attached to a Navy Sea, Air, and Land (SEAL) Team conducting reconnaissance operations in Takur Ghar, Afghanistan, on March 4, 2002. During insertion, the team's helicopter was ambushed causing a teammate to fall into an entrenched group of enemy combatants below. Sergeant Chapman and the team voluntarily reinserted onto the snow-capped mountain, into the heart of a known enemy stronghold to rescue one of their own. Without regard for his own safety, Sergeant Chapman immediately engaged, moving in the direction of the closest enemy position despite coming under heavy fire from multiple directions. He fearlessly charged an enemy bunker, up a steep incline in thigh-deep snow and into hostile fire, directly engaging the enemy. Upon reaching the bunker, Sergeant Chapman assaulted and cleared the position, killing all enemy occupants. With complete disregard for his own life, Sergeant Chapman deliberately moved from cover only 12 meters from the enemy, and exposed himself once again to attack a second bunker, from which an emplaced machine gun was firing on his team. During this assault from an exposed position directly in the line of intense fire, Sergeant Chapman was struck and injured by enemy fire. Despite severe, mortal wounds, he continued to fight relentlessly, sustaining a violent engagement with multiple enemy personnel before making the ultimate sacrifice. By his heroic actions and extraordinary valor, sacrificing his life for the lives of his teammates, Technical Sergeant Chapman upheld the highest traditions of military service and reflected great credit upon himself and the United States Air Force.