Michael was born on the 23rd of March 1949, in Greenville South Carolina, and enlisted in the US Navy after graduating from high school. The first year of his enlistment comprised of boot camp and service on board some Navy destroyers. He then attended the US Navy SEAL selection and training at Coronado, California, and he graduated with BUD/S class 49 in March of 1969. Michael was then assigned to SEAL Team 1 and then deployed to the Republic of Vietnam after additional SEAL training. From December 1969 to December of 1972, he was deployed to the region at least seven times, and Michael was a Petty Officer and one of only a dozen of Navy SEALs still in the country. It was his actions on the 31st of October 1972, that would 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 participating in a daring operation against enemy forces. PO Thornton, as assistant U.S. Navy adviser, along with a U.S. Navy lieutenant serving as senior adviser, accompanied a three-man Vietnamese Navy SEAL patrol on an intelligence-gathering and prisoner capture operation against an enemy-occupied naval river base. Launched from a Vietnamese Navy junk in a rubber boat, the patrol reached land and was continuing on foot toward its objective when it suddenly came under heavy fire from a numerically superior force. The patrol called in naval gunfire support and then engaged the enemy in a fierce firefight, accounting for many enemy casualties before moving back to the waterline to prevent encirclement. Upon learning that the senior adviser had been hit by enemy fire and was believed to be dead, PO Thornton returned through a hail of fire to the lieutenant's last position, quickly disposed of two enemy soldiers about to overrun the position, and succeeded in removing the seriously wounded and unconscious Senior Naval Advisor to the water's edge. He then inflated the lieutenant's lifejacket and towed him seaward for approximately two hours until picked up by support craft. By his extraordinary courage and perseverance, PO Thornton was directly responsible for saving the life of his superior officer and enabling the safe extraction of all patrol members, thereby upholding the highest traditions of the U.S. Naval Service.

The US Navy Lieutenant mentioned in the citation is fellow Navy SEAL Thomas Norris. Not mentioned in the citation was one of the Vietnamese men that was along for the mission. Not only did Michael swim with Thomas Norris, but he also had grabbed one of the Vietnamese that had been injured and swam with them both for more than two hours. One of the South Vietnamese special forces soldiers was picked up in the water by one of their boats and he reported that the two Americans were dead. The USS Newport News left once they heard the report and Michael and Thomas were only picked up after Michael fired an AK-47 into the air for attention. They were transported to the Newport News and Michael carried Thomas into the operating room on board.

Michael received the Medal of Honor from President Nixon on the 15th of October 1973, in a ceremony at the White House. Even though Michael was told that Thomas wouldn’t survive, he in fact did and received the Medal of Honor in 1976, but that is a story for another time. Michael remained in the Navy after the war and returned to Coronado as a BUD/S instructor from 1974 to 1977. He was selected by Commander Richard Marcinko in 1980 to be a founding member of SEAL Team 6 and he received a commission as a limited duty officer in 1982. The last conflict that he served in was as a company commander for a rapid response deployment in support of Desert Shield/Desert Storm in 1990. Two years later, he retired at the rank of Lieutenant after 25 years of service. In addition to the Medal of Honor, he was also awarded the Silver Star, three Bronze Stars with valor, and two Purple Hearts. Michael Edwin Thornton was the last recipient to be serving on active duty at the time of his retirement and he is one of two recipients named Michael Thornton (the other was a Seaman who received the Medal of Honor for actions in 1881).