Jack Bayard was born on Earth. Bayard would later join the Earth Federation Army as an officer cadet in U.C. 0077 and was sent to the Earth Federation Officer School. He graduated on U.C. 0079 and was commissioned as a lieutenant. During the One Year War in U.C. 0079, the Earth Federation Forces enact a training program for soldiers in the regular army to become mobile suit pilots. Jack, also being one of these new MS pilots, displayed excellent technical aptitude and piloting skills. On December 20 of the same year, Jack was promoted to Second Lieutenant and later served alongside Adam Stingray on the Salamis kai (SCRT-229 Suruga), where he was captain of an MS squad and first received his own MS, an RGM-79 GM emblazoned with his personal "Jack-o'-lanterns with a sickle" emblem and would come to be known as "Jack The Halloween". On December 24, Jack is deployed for first the time in actual combat to participate in the EFF's Operation Cemballo to attack the space fortress Solomon. Jack would also participate in Operation Star One, where the Suruga would be sunk when the Principality of Zeon fires the Solar Flare colony laser on the EFF space fleet converging on the asteroid A Baoa Qu, fortunately he survives along with Adam aboard the Suruga's escape launch. He has also commanded an MS platoon aboard a Waj-class Earth Federation transport. After the war, he was hired by Anaheim Electronics in U.C. 0082 as a test pilot for the RX-78GP00 Gundam GP00 "Blossom".
He would later appear in the manga École du Ciel. Unlike Kamille Bidan, who entered AEUG as a civilian, Jack entered AEUG as a professional Federation MS pilot, sent to the lunar city of Anman in U.C. 0087 to test the capabilities of a captured Titans RX-178 Gundam Mk-II. He holds contempt for, and clashes with Marie Albertia's "pirates", who were also involved in the Gundam testing. During the Gryps Conflict, He later serves as leader of the Halloween MS squad aboard the Irish-class battleship Zwickbau.
- While unconfirmed, sources site the origin of Jack Bayard's nickname to be associated with his birthday, which was on the holiday of Halloween (October 31).
- Jack's stylized emblem also takes inspiration from the traditional Jack-o'-lantern.