George was born on the 23rd of February 1875, in Phillipsburg, New Jersey, where he grew up as the second oldest of six children. He enlisted in the US Navy was an Apprentice First Class on board the USS Marblehead when he deployed to Cuba in support of the Spanish-American War. It was his actions during the severing of an underwater communications cable that would later earn him the Medal of Honor. The citation reads:

On board the U.S.S. Marblehead during the operation of cutting the cable leading from Cienfuegos, Cuba, 11 May 1898. Facing the heavy fire of the enemy, Mager displayed extraordinary bravery and coolness throughout this action.

George was presented the Medal of Honor on the 2nd of November 1899, and not much else is known about his military career. He was married to Ella and the couple had three children, while working as a machinist at the John A Roebling’s Sons Company in Trenton, New Jersey. George Frederick Mager died at the age of 63 on the 12th of April 1938, and he is buried with his wife in the Greenwood Cemetery in Hamilton, New Jersey: Division NW, Section P, Lot 12, Grave 1.