Gregory Mahoney was a soldier in the United States Army who received the Medal of Honor for gallantry in action during the Indian Wars.
Mahoney was born in Pontypool in South Wales. He emigrated to the United States and joined the U.S. Army at Boston, Massachusetts and was assigned to the 4th Cavalry Regiment.
On September 26, 1874 he was part of a cavalry detachment dispatched to locate a large group of Native Americans of the Cheyenne tribe near the Red River in Texas which was ambushed. A seven-hour battle followed as the cavalry withdrew to the north rim of Tule Canyon. Over the following two days, a number of actions between the opposing forces continued, during which three men of the Fourth Cavalry earned Medals of Honor, each of them cited for "Gallantry in action" on September 26–28, 1874.
Private Mahoney served throughout this action, but was specifically cited for his actions on September 27 when, with Corporal Edwin Phoenix and Private Ernest Veuve, far in advance of the rest of their unit, the three men attacked a large group of Cheyenne warriors which were attempting to stampede the cavalry's tethered horses.
Mahoney's later life and date of death are unknown. There is a cenotaph in his honor at Fort Concho National Historic Landmark.