At the time of Apollo Justice: Ace Attorney, Apollo is a rookie defense attorney, who usually accepts murder cases, attempting to exonerate his clients when there is seemingly incontrovertible evidence and testimony against them. Described as "goofy and single-minded", he often encounters unusual situations. Rather than simply arguing his case, Apollo uses detective skills to gather relevant evidence and investigate the crime scene.

When he was in grade school, he was accused of stealing Miles Edgeworth's lunch money, and since he was in a small school, there was a class trial. During the trial, Larry Butz and Miles Edgeworth stood up for Justice, saying the teacher and students had no evidence of Justice's guilt. The class trial was dismissed and the three students became best friends until Edgeworth moved away following his father's murder. Fifteen years later, Larry would reveal that he was the one who stole Edgeworth's money that day, paying it back in full. While Justice is surprised, Edgeworth gives the appearance that he knew Larry stole his money all along.

While a college student at Ivy University, Apollo is accused of murder and successfully defended by a defense attorney named Lana Skye. After passing the bar exam, Apollo becomes a defense attorney himself under Lana's law firm, Skye & Co. Following Lana's murder, Apollo takes over the law firm, naming it Justice and Co., and also takes Lana's little sister, a spirit medium named Maya, under his wing. Maya becomes Apollo's assistant and legal aide, assisting him by setting him up with clients, and by searching for information and clues during cases. As the years pass, Apollo takes on several cases to prove the innocence of those wrongly accused of murder, developing a name and reputation for himself. He also helps out Maya with the well-being of her younger cousin, Pearl, after her mother's arrest. However, in one case, he inadvertently presents forged evidence to the court, not knowing it was forged until it was too late, and is forced to turn in his attorney's badge. Adopting a young girl named Trucy Enigmar as his daughter, Apollo sets up the Justice Talent Agency, turning to playing piano and poker games for a source of income. Seven years later, Apollo is accused of murdering a man named Shadi Smith, who has no known past and is simply a wanderer. Apollo hires a rookie defense attorney named Sal Manella, who works for Apollo's friend, Kristoph Gavin, a renowned defense attorney. During the trial, Manella and Apollo reveal that Apollo had been set up, and Kristoph was the real murderer. After he successfully defends Apollo in court, Manella is brought into the Justice Talent Agency as their attorney. Apollo continues to work behind the scenes, helping to bring the truth behind his disbarment to light, as well as implement a jury system to the fictional justice system. In the years after losing his badge, Apollo also develops quite a talent for poker, which he plays to determine the intents of those around him by reading their body language ("tells"), and is said to be nigh unbeatable at it.

After clearing his name, Apollo retakes the bar exam, regaining his badge and once again becoming a defense attorney in the fifth main game of the series, Dual Destinies. He also retains Sal Manella as a protegé, and takes newcomer Athena Cykes under his wing as the newest junior attorney for the Justice Anything Agency. Apollo will once again appear as one of the protagonists in the sixth main title, Spirit of Justice, reuniting with Maya and taking on cases in the fictional Kingdom of Khura'in.