Not much is known of the life of James Darrell Edwards III prior to being recruited to MIB. His appearance as a small child in 1969 in Men in Black 3 would place his year of birth in 1965. His father, United States Army Colonel James Darrell Edwards II, was working security at Kennedy Space Center for the Apollo 11 launch when he was murdered by Boris the Animal after assisting Agent K in stopping a chain of events that would have led to K's death and a widescale invasion of Earth forty years later. Although young James was present at the event, K uses the neuralyzer on the young boy, saying his father was a hero. James was left with his father's pocket watch to remember him by. Nothing else is known about the preceding twenty-eight years save that James became an accomplished police officer with the NYPD. It does not appear as if he had any family by the mid-1990s.
Though little is known of J's personal life outside of his role as an agent of Men in Black, he is known to be a big fan of both video games, which he is seen playing in his off hours, and rap music. A line of dialogue from Men in Black II suggests he owned a Game Boy.
Agent J's MIB career starts out when, as NYPD officer James Edwards, he runs down a swift, wall-climbing alien on foot. When MIB Agent K notices his potential, he recruits J into the MIB (within the continuity of the series, the events of Men in Black 3 imply that K recognized J from their meeting in the 60s). At first, J is suspicious, but he decides to join. He is registered as Agent J and his energetic, enthusiastic attitude brings humor to a bland organization. J is not fond of K's diminutive references to him (son, sport, slick, kid, etc.), but gets used to it. In his various adventures, he encounters Frank, the dog; finds out that Jeebs, the pawn store owner is actually an alien, not just a buyer of stolen goods from chain snatchers like he originally thought when he was a detective; and delivers a baby squid. Their first official mission is to stop an alien Bug from leaving Earth with a tiny galaxy before the galaxy's owners disintegrate the planet. During the final confrontation with the bug, K is swallowed by it in an attempt to get his gun back, leaving J to keep him on Earth. When he starts squishing cockroaches, the Bug confronts him, but before it can attack him, K shoots it from the inside. The Bug was finally killed by Dr. Laurel Weaver (Linda Fiorentino), a morgue worker. When K requests to be neutralized (a memory-wiping procedure) to retire, J fulfills the request and his new partner is Laurel, who becomes known as Agent L.
At some point between the first and second film, L goes back to her morgue career, and J has gained a reputation for neutralizing all of her successors for, in his opinion, unsuitability to work at MiB; at the beginning of the film, he neutralizes his new partner Agent T because he forces T to admit that he joined the agency to be a hero, something that is fundamentally impossible in the Men in Black due to the secretive nature of the organization. Other than that, he has developed into a superb and highly respected agent. When he is sent to get K back to face a new threat to which only he had details of locked away in his mind, J's temporary partner is an alien disguised as a talkative pug, Frank. J investigates a murder at a local pizza joint committed by Serleena, the Kylothian queen who has arrived to find the Light of Zartha after destroying several planets. During the investigation, he meets and falls in love with an employee named Laura Vasquez. Despite the MIB's policy, J does not neuralyze her. J then heads to find Kevin Brown who holds the key to finding the Light of Zartha and stopping Serleena before she could get her hands on the Light. When K is de-neuralyzed, J is once again the rookie, but for revenge, J gives K the Noisy Cricket (the tiny gun that K saddled him with in the first movie, though it does have a strong blast). The duo discover the light is Laura, and J (reluctantly) allows her to fulfill her destiny as he and K finally destroy Serleena for good.
During the film, J has a particular enmity with the alien criminal known as Jara, whom J stopped from stealing the Earth's ozone layer.