Michael was born in County Claire, Ireland in 1839 and like others within the Korean Expedition, not much is known about his life. We know that it was his time in the US Marine Corps that would earn him the Medal of Honor. The citation reads:
While serving on board the U.S.S. Benicia, for gallantry in advancing to the parapet, wrenching the match-lock from the hands of an enemy and killing him, at the capture of the Korean Forts, June 11, 1871.
Michael McNamara died on the 25th of April, 1907 and is buried in the Holy Name Cemetery in Hoboken, New Jersey: Block I, Section G, Grave 29-30.