John Donnelly was born on October 20, 1949, in Philadelphia, Pennsylvania. He enlisted in the U.S. Navy on June 10, 1968, and went on active duty to begin basic training on October 1, 1968. SN Donnelly completed basic training at NTC Great Lakes, Illinois, in December 1968, and completed Basic Underwater Demolition/SEAL training with Class 050 at NAB Coronado, California, in May 1969. His first assignment was with SEAL Team ONE at NAB Coronado from May 1969 to February 1970, and then deployed with his Team to South Vietnam from March 1970 until he was killed in a helicopter crash on June 23, 1970. John Donnelly was buried at the Holy Cross Cemetery in Yeadon, Pennsylvania.

His Bronze Star Medal w/Valor Citation reads:

For meritorious service while serving with friendly foreign forces engaged in armed conflict against the North Vietnamese and Viet Cong communist aggressors in the Republic of Vietnam from 5 March to 23 June 1970. While serving as radioman with United States Navy SEAL Team One, Detachment Golf, Echo Platoon, Seaman Donnelly participated in fifty-five combat missions in Viet Cong dominated areas of the Mekong Delta. His skill in using his radio significantly contributed to the success of those operations against the enemy. While operating in the field, he continuously exhibited an aggressive spirit and loyalty to his fellow patrol members. On 5 May 1970, his platoon was proceeding south on the Ong Quyen canal when it suddenly came under heavy enemy rocket and automatic weapons attack. Reacting immediately, Seaman Donnelly climbed to the port machine gun mount and returned the attack with highly accurate grenade fire. At that moment, the craft took a direct enemy rocket hit which inflicted him with multiple shrapnel wounds. Recovering quickly, he administered first aid to the wounded men about him. His selfless actions were instrumental in saving the life of one of his shipmates. Seaman Donnelly's exemplary professionalism, devotion to duty and courage under fire reflected great credit upon himself and were in keeping with the highest traditions of the United States Naval Service.