Small for his age and very headstrong, Armed's habit of biting and kicking hay out of his handler's pitchfork, along with being practically untrainable, caused his trainer, Ben A. Jones to send him back to Calumet Farm to be gelded and turned out to grow up. He returned to the track late in his two-year-old season and resumed training.
His first start was as a three year old the following February and he won at Hialeah Park by eight lengths. He won again less than a week later but then won only once in five starts and had to be rested due to an ankle injury.
Armed raced for seven seasons from 1944 to 1950, finishing with a 41-20-10 record in 81 starts. In a season that saw him defeat U.S. Triple Crown champion Assault in a match race at Belmont Park, Armed also set a new track record of 2:01-3/5 for one and one-quarter miles while winning the Widener Handicap and carrying 129 pounds, and earned the 1947 Horse of the Year honors.
In 1963, Armed was inducted into National Museum of Racing and Hall of Fame. In The Blood-Horse ranking of the top 100 U.S. thoroughbred champions of the 20th Century, he was ranked #39.