Harold was born on the 29th of January, 1925 in Racine, Wisconsin. He briefly worked for the Rench Manufacturing Company as a multigraph operator and at the age of 17, he enlisted in the US Marine Corps. Harold completed his recruit training in San Diego at the Marine Corps Recruit Depot and was then assigned to Headquarters and Service Battery, 4th Battalion, 10th Marines, of the 2nd Marine Division. He deployed to New Zealand on the 3rd of November, 1942 and trained for the next eleven months in Wellington.

Harold took part in the fighting on Betio Island as a private first class and then went to the Hawaiian Islands with the 2nd Marine Division to train for the invasion of Saipan. He landed on Saipan on the 10th of June, 1944 and the fighting went on for three weeks when the enemy launched a counter attack on the 7th of July. It was on this day that Harold's actions would later earn him the Medal of Honor. The citation reads:

For conspicuous gallantry and intrepidity at the risk of his life above and beyond the call of duty while serving with the 4th Battalion, 10th Marines, 2nd Marine Division, in action against enemy Japanese forces on Saipan, Marianas Islands, July 7, 1944. When the enemy launched a fierce, determined counterattack against our positions and overran a neighboring artillery battalion, PFC Agerholm immediately volunteered to assist in the efforts to check the hostile attack and evacuate our wounded. Locating and appropriating an abandoned ambulance jeep, he repeatedly made extremely perilous trips under heavy rifle and mortar fire and single-handedly loaded and evacuated approximately forty-five casualties, working tirelessly and with utter disregard for his own safety during a grueling period of more than three hours. Despite intense, persistent enemy fire, he ran out to aid two men whom he believed to be wounded Marines but was himself mortally wounded by a Japanese sniper while carrying out his hazardous mission. PFC Agerholm's brilliant initiative, great personal valor and self-sacrificing efforts in the face of almost certain death reflect the highest credit upon himself and the U.S. Naval Service. He gallantly gave his life for his country.

Harold's mother received his posthumous Medal of Honor from the Commandant of the Ninth Naval District in a private ceremony, a request she had made for no public presentation. A US destroyer, a combined elementary/middle school in Racine, and a Gun Park near the 10th Marine Regiment headquarters in Camp Lejeune, North Carolina, were all named in honor of the 19 year old Harold. Originally buried in the 2nd Marine Division cemetery in Saipan, Harold Christ Agerholm is now buried in the Mound Cemetery in Racine, Wisconsin; Block 4-E, Lot 8, Grave 4.