John Marcum was born on September 25, 1973, in Flushing, Michigan. He enlisted in the U.S. Navy on August 5, 1991, and completed basic training at NTC San Diego, California, in October 1991. Petty Officer Marcum next attended Intelligence Specialist "A" School at Dam Neck Annex, Virginia, from November 1991 to March 1992, followed by Basic Underwater Demolition/SEAL training at NAB Coronado, California, from April 1992 to February 1993. His first assignment was with SEAL Team TWO at NAB Little Creek, Virginia, from April 1993 to May 2000, and during this time he deployed to Stuttgart, Germany, with Naval Special Warfare Unit TWO from March to September 1996, and to Sarajevo, Bosnia/Herzegovina in support of Operation Joint Guard from February to March 1998. Senior Chief Marcum's final assignment was with Naval Special Warfare Development Group at Dam Neck Annex from March 2000 until he was killed in action in Afghanistan on September 11, 2008. During this time he deployed multiple times in support of Operation Enduring Freedom in Afghanistan and Operation Iraqi Freedom. He was buried at the Colonial Grove Memorial Park in Virginia Beach, Virginia.

His 4th Bronze Star w/Valor Citation reads:

For heroic achievement in connection with combat operations against the enemy as Assault Team Leader for a Joint Task Force in direct support of Operation IRAQI FREEDOM from 4 January to 11 April 2007. Chief Petty Officer Marcum skillfully employed his multi-man assault team and enablers during the execution of multiple dashing direct action missions in uncertain environments resulting in the elimination or capture of numerous suspected terrorists. During the execution of these missions, he repeatedly exposed himself to enemy threats and improvised explosive devices. His quick thinking and tactical expertise were essential as his team was often engaged in close quarters combat. In one action, he was directly responsible for engaging armed enemy combatants before they had the opportunity to engage his assault troops. His superb leadership and exceptional performance significantly degraded the enemy's effectiveness and contributed greatly to his Task Force's primary mission to capture and eliminate terrorist fighters. By his extraordinary guidance, zealous initiative, and total dedication to duty, Chief Petty Officer Marcum reflected great credit upon himself and upheld the highest traditions of the United States Naval Service.

The Combat Distinguishing Device is authorized.