Carpenter was born in Jackson, Mississippi on October 17, 1989, and raised in Flowood by his parents Robert and Robin. He enlisted in the Marine Corps' delayed entry program at age 19 in February 2009, and completed Recruit Training in July 2009 at Marine Corps Recruit Depot, Parris Island, South Carolina. After his July 2013 medical retirement, Carpenter enrolled at the University of South Carolina in Columbia, said to be pursuing a degree in international studies. He is a 2013 initiate of the Chi-Omega chapter of the Kappa Sigma Fraternity at the University of South Carolina.
After completing his initial training at the Camp Geiger School of Infantry, Marine Corps Base Camp Lejeune, North Carolina, Private First Class Carpenter was assigned to Fox Company, 2nd Battalion, 9th Marines, Regimental Combat Team One, 1st Marine Division (Forward), 1st Marine Expeditionary Force (Forward), in Helmand Province, Afghanistan in support of Operation Enduring Freedom on 21 November 2010, where he served as a Squad Automatic Weapon (SAW) gunner from September 2009 to November 2010.
In July 2010, Lance Corporal Carpenter deployed to Marjah, Helmand Province, Afghanistan, in support of Operation Enduring Freedom. On November 21, 2010, while joining his team to fight off a Taliban attack in a small village, he suffered severe injuries to his face and right arm from the blast of an enemy hand grenade, including multiple shrapnel wounds and the loss of his right eye. After-action reports state that he threw himself in front of the grenade to protect a fellow Marine, Lance Cpl. Nick Eufrazio.
Carpenter's former battalion commander, Lt. Col. James Fullwood, told Marine Corps Times in a story published in January 2012 that the Corps was still investigating what happened the day Carpenter and Eufrazio were injured:
The actions that happened on that roof are definitely a matter of interest. We've never, from that day until now, stopped trying to uncover what took place, whether it be for reasons of identifying someone who deserves to be recognized with an award or to understand more about the events that unfolded.
In March 2011, the South Carolina legislature passed a resolution recognizing Carpenter's service, noting that he "suffered catastrophic wounds in the cause of freedom" and "has shown himself worthy of the name Marine."
As a patient then attached to Wounded Warrior Battalion East, Bethesda, Maryland on Thursday, November 10, 2011, he participated in the Ribbon Cutting Ceremony at the dedication of the newly integrated Walter Reed National Military Medical Center with then United States Secretary of Defense Leon Panetta.
On June 19, 2014, Corporal Carpenter was awarded the Medal of Honor in a ceremony at the White House. 
He is the eighth living recipient to be awarded the Medal of Honor for actions in Iraq or Afghanistan. Carpenter served as an Automatic Rifleman with Company F, 2d Battalion, 9th Marines, Regimental Combat Team-1, 1st Marine Division (Forward), I Marine Expeditionary Force (Forward). In July 2013, he was medically retired as a Corporal due to his wounds. Carpenter is credited with attempting to shield a fellow Marine, Lance Cpl. Nick Eufrazio, from Plymouth, Massachusetts, from a grenade blast on a rooftop security post in combat operations near Marjah, Helmand Province, Afghanistan on November 21, 2010. Both Marines survived the blast but suffered major injuries. Carpenter lost his right eye and most of his teeth. His jaw and right arm were shattered and he has undergone dozens of surgeries.
The President of the United States of America in the name of The Congress takes pleasure in presenting the MEDAL OF HONOR to
LANCE CORPORAL WILLIAM KYLE CARPENTER
UNITED STATES MARINE CORPS
Medal of Honor Official Citation reads:
For conspicuous gallantry and intrepidity at the risk of his life above and beyond the call of duty while serving as an Automatic Rifleman with Company F, 2d Battalion, 9th Marines, Regimental Combat Team 1, 1st Marine Division (Forward), I Marine Expeditionary Force (Forward), in Helmand Province, Afghanistan, in support of Operation Enduring Freedom on 21 November 2010. Lance Corporal Carpenter was a member of a platoon-sized coalition force, comprised of two reinforced Marine rifle squads partnered with an Afghan National Army squad. The platoon had established Patrol Base Dakota two days earlier in a small village in the Marjah District in order to disrupt enemy activity and provide security for the local Afghan population. Lance Corporal Carpenter and a fellow Marine were manning a rooftop security position on the perimeter of Patrol Base Dakota when the enemy initiated a daylight attack with hand grenades, one of which landed inside their sandbagged position. Without hesitation and with complete disregard for his own safety, Lance Corporal Carpenter moved toward the grenade in an attempt to shield his fellow Marine from the deadly blast. When the grenade detonated, his body absorbed the brunt of the blast, severely wounding him, but saving the life of his fellow Marine. By his undaunted courage, bold fighting spirit, and unwavering devotion to duty in the face of almost certain death, Lance Corporal Carpenter reflected great credit upon himself and upheld the highest traditions of the Marine Corps and the United States Naval Service.
Carpenter appeared in a video, "Still in the Fight," to raise money for the Fisher House Foundation, which provides free and low-cost housing to veterans and families receiving treatment at military hospitals.