Terry was born in Gotham City on August 18, 2023 to Warren and Mary McGinnis. In his early teens he belonged to a street gang lead by Charles "Big Time" Bigelow, and once served a three month stint in juvenile hall.
Years later, while attempting to escape from The Jokerz he found himself at the gate of Bruce Wayne. Despite his old age Bruce managed to help Terry fight off his attackers, before he colapsed to the ground, and McGinnis then carried Mr. Wayne back to his mansion so he could take his medication. Shortly after taking his medicine Bruce Wayne fell asleep and Terry decided to snoop around. He noticed a bat stuck in an old grandfather clock. When he tried to free the animal he stumbled upon the entrance to the Batcave.
Bruce was furious with Terry when found him snooping around the Batcave, and kicked him out. When Terry finally returns home he discovers that his father has been murdered and that the police think The Jokerz are responisble. He investigates on his own and discovers that Derek Powers is actually the one responsible. He rushes back to Wayne's mansion and asks his assistance in bringing Powers to justice, but Bruce reminds young McGinnis that he has given up the cape and cowl. For good.
Not one to give up Terry then decides to take matters into his own hands and sneaks into Wayne Manor to steal the Bat suit for himself. When Bruce discovers that the suit is missing he shuts it down, with Terry inside, in the middle of a battle. Terry pleads with Bruce to help him confront Powers because he thinks he can prove who was really behind the death of his father. Bruce reluctantly releases control of the suit to Terry.
Convinced that there is still a need for a Batman, Bruce hires Terry as his "personal assistant" and begins secretly training him for his new role as Batman. In addition, Bruce assists Terry in the field primarily by keeping in continual contact with the boy at the Batcave.
After Powers' criminal identity is revealed to the public and he finally brings retribution to his father's killers, Terry decides to continue his role as Batman to make up for his past sins, in hope that his heroic role is his chance at redemption. As a student, he aspires of being a doctor, but his past always comes into his mind. Even though Bruce decides to fight crime after his parents were murdered, Terry has a different reason to continue; before Warren was murdered, Terry always felt guilty about letting his family and friends down because of his past as a juvenile delinquent. Because of this, he always tries to find a way to make up for what he's done – trying his best at school, joining athletic teams, and helping others, in the hope that someday people will see him differently. Terry originally assumed the role of Batman for his father, but eventually sees it as a chance to help people and to look like a worthwhile human being again, in his own eyes if in no one else's.
The Justice League Unlimited episode "Epilogue" reveals that Terry is Bruce's biological son due to Amanda Waller's "Batman Beyond" project. The project caused Terry's father to have his reproductive DNA overwritten and made Bruce's reproductive DNA dominant when Warren McGinnis took a fake flu shot. This makes Bruce the biological father of both Terry and his brother Matt, even if Warren McGinnis raised them.