Jimmy is a young man from South Dakota who becomes an unlikely participant in the conflict between Autobots and Decepticons. He enters this world by answering a want ad placed by Cade Yeager, who was seeking an extra hand to watch his junkyard while away on missions. The promise of being named the Senior Vice President of the company lured Jimmy into the position, though the reality of the job turned out to be far different from what he expected. His primary responsibilities essentially involved trying to maintain a fragile peace among the boisterous Autobots who called the junkyard their home, a task that proved nearly impossible given their cantankerous dispositions. Cade rarely paid him any actual wages, instead claiming that Jimmy's compensation came from serving the greater good. He often found himself on the receiving end of Cade's verbal abuse, serving as a target for his employer to blow off steam after many failed missions.

In terms of personality, Jimmy comes across as overwhelmed and hapless, constantly struggling to cope with the absurdity of dealing with giant alien robots and a tyrannosaur-sized mechanical dinosaur named Grimlock, who had previously attempted to eat him. He is prone to panic and dramatic outbursts, often crying out in distress when danger approaches. When a drone and a warning alerted the group to an impending Decepticon attack, Jimmy panicked and desperately cried that he was too skinny for jail. His dramatic tendencies reach their peak during a skirmish where he gets shot with a bean bag from a drone. Believing his wounds to be fatal, he attempted to bid a heartfelt and dramatic farewell to Cade, only to discover that he had been hit by a non-lethal projectile. Despite his whining and complaining, he demonstrates a degree of loyalty by helping Cade collect weapons and assisting in the group's escape, though he also has a self-interested side, as shown when he allowed a character named Daytrader entry into the junkyard in exchange for a Cybertronian weapon for himself. Jimmy also tussled with the diminutive Autobot Wheelie after being called out for this deal.

Jimmy's role in the story is primarily that of a comic relief character who provides a human perspective on the sheer chaos surrounding Cade and the Autobots. He is present during the Decepticon assault on the junkyard, helps the group escape into a nearby town, and later returns to the junkyard with other characters. When Cybertron appears in Earth's sky, Jimmy is alerted to the news by a young ally and accompanies the Autobots on a ship to England, where he happily reunites with Cade and expresses exhilaration at seeing Optimus Prime. During the final battle, he observes from the safety of the Autobot ship.

Jimmy's key relationships center on Cade Yeager, his employer and primary source of frustration. He also interacts with several Autobots, particularly Hound, whose bombastic arrivals and cluster bombs irritate Jimmy by stirring up dust. He shares scenes with Wheelie, with whom he was passing time looking at vehicle websites. He forms a connection with a young woman named Izabella and later with the Autobot Crosshairs, who assumes command of the junkyard crew in Cade's absence. He has a notable encounter with Cogman, which nearly gets Cade killed amidst the chaos of a drone attack.

Throughout the film, Jimmy undergoes a modest development from a frightened, overwhelmed employee who complains about the wild kingdom the junkyard becomes in Cade's absence to someone who willingly accompanies the group to England and participates in the larger mission. While he remains fearful and dramatic, he ultimately chooses to stay with the group rather than flee entirely when given opportunities to do so.

Regarding notable abilities, Jimmy possesses no superpowers or specialized combat training. His abilities are entirely mundane, consisting of basic manual labor skills for maintaining a junkyard and the capacity to drive or travel with the Autobot-aligned humans. His most notable skill might be his self-preservation instinct, though his dramatic nature frequently exaggerates the level of danger he is actually in. He is, as he himself points out, simply someone hired from a newspaper advertisement without any extraordinary capabilities. Jimmy serves as a reminder of how an ordinary person might react when thrust into an extraordinary war between giant alien robots.