James Diamond was born on April 22, 1925, in New Orleans, Louisiana. He was raised in Gulfport, Mississippi, and enlisted in the U.S. Army at Camp Shelby, Mississippi, on September 7, 1943. PFC Diamond next attended basic training and infantry training before deploying with his unit to the Pacific in 1944. He served with Company D, 21st Infantry Regiment of the 24th Infantry Division in the Pacific, and participated in the invasion of the Philippines in late 1944 and early 1945. During the liberation of Mindanao, PFC Diamond was killed in action at the battle of Mintal on May 14, 1945. He was posthumously awarded the Medal of Honor on March 6, 1946, for his heroism during the battle. James Diamond was buried at the Evergreen Cemetery in Gulfport, Mississippi, and he was inducted into the Louisiana Military Hall of Fame on November 13, 2010.

His Medal of Honor Citation reads:

As a member of the machinegun section, he displayed extreme gallantry and intrepidity above and beyond the call of duty. When a Japanese sniper rose from his foxhole to throw a grenade into their midst, this valiant soldier charged and killed the enemy with a burst from his submachine gun; then, by delivering sustained fire from his personal arm and simultaneously directing the fire of 105mm. and .50 caliber weapons upon the enemy pillboxes immobilizing this and another machinegun section, he enabled them to put their guns into action. When 2 infantry companies established a bridgehead, he voluntarily assisted in evacuating the wounded under heavy fire; and then, securing an abandoned vehicle, transported casualties to the rear through mortar and artillery fire so intense as to render the vehicle inoperative and despite the fact he was suffering from a painful wound. The following day he again volunteered, this time for the hazardous job of repairing a bridge under heavy enemy fire. On 14 May 1945, when leading a patrol to evacuate casualties from his battalion, which was cut off, he ran through a virtual hail of Japanese fire to secure an abandoned machine gun. Though mortally wounded as he reached the gun, he succeeded in drawing sufficient fire upon himself so that the remaining members of the patrol could reach safety. Pfc. Diamond's indomitable spirit, constant disregard of danger, and eagerness to assist his comrades, will ever remain a symbol of selflessness and heroic sacrifice to those for whom he gave his life.