Frank was born on the 19th of August, 1921, in Indian Gap, Texas. After graduating from Roaring Springs High School in 1938, he enlisted in the US Marine Corps and served aboard the USS Enterprise in the Pacific during World War 2. Frank was commissioned as a Second Lieutenant in 1945 and attended Colorado College, Southwestern University, and North Texas Agricultural and Mechanical College under the Navy V-12 program, which was a program designed to produce officers that were technically trained in specific fields.

When Frank had deployed to Korea, he was a First Lieutenant and it was his actions during the Battle of Chosin Reservoir that would cost him his life and 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 as Leader of a Rifle Platoon of Company A, First Battalion, Seventh Marines, First Marine Division (Reinforced), in action against enemy aggressor forces in Korea on 26 November 1950. Leading his platoon in point position during a patrol by his company through a thickly wooded and snow-covered area in the vicinity of Hasan-ni, First Lieutenant MITCHELL acted immediately when the enemy suddenly opened fire at point-blank range, pinning down his forward elements and inflicting numerous casualties in his ranks. Boldly dashing to the front under blistering fire from automatic weapons and small arms, he seized an automatic rifle from one of the wounded men and effectively trained it against the attackers and, when his ammunition was expended, picked up and hurled grenades with deadly accuracy, at the same time directing and encouraging his men in driving the outnumbering enemy from his position. Maneuvering to set up a defense when the enemy furiously counterattacked to the front and left flank, First Lieutenant MITCHELL, despite wounds sustained early in the action, reorganized his platoon under devastating fire and spearheaded a fierce hand-to-hand struggle to repulse the onslaught. Asking for volunteers to assist in searching for and evacuating the wounded, he personally led a party of litter bearers through the hostile lines in growing darkness and, although suffering intense pain from multiple wounds stormed ahead and waged a singlehanded battle against the enemy, successfully covering the withdrawal of his men before he was fatally struck down by a burst of small-arms fire. Stouthearted and indomitable in the face of tremendous odds. First Lieutenant MITCHELL by his fortitude, great personal valor and extraordinary heroism, saved the lives of several Marines and inflicted heavy casualties among the aggressors. His unyielding courage throughout reflects the highest credit upon himself and the United States Naval Service. He gallantly gave his life for his country.

Frank's Medal of Honor was presented to his wife and daughter in their house in Atlanta, Georgia, on the 6th of August, 1952, by the acting director of the 6th Marine Corps Reserve District. Frank Nicias Mitchell is buried in the Roaring Springs Cemetery in Roaring Springs, Texas: IMO – Center Section, Row D.