Jim Paxton is a police officer who is engaged to Maggie Lang, the ex-wife of Scott Lang. In 2015, Paxton was surprised to see Lang attend the birthday party of Cassie, as Lang had not sent money for the education of Cassie. After the party, he accompanied Cassie to say goodbye to her father. Two nights after Scott was arrested for breaking into a house and was taken to police headquarters where Paxton worked. He told Lang that he was disappointed because he thought he had really changed. He further said that this news would devastate Cassie and Maggie. The conversation ended when Gale, Paxton's partner arrived and informed Lang that his lawyer wanted to talk to him.
Minutes later, Paxton and Gale began a chase on Lang as this one had escaped from his cell. The next day, Paxton was having breakfast with Maggie and Cassie, who said she did not want him to find her dad. During breakfast, Gale called him to inform him that Lang's lawyer was indeed the renowned businessman and scientist Hank Pym. With this information, he and Gale went to Pym Technologies to interview with Hank Pym; however they were interrupted by Kurt and Dave, who decided to steal the car of both to allow Pym meet with Darren Cross. Already away from Pym, Paxton heard the sound of a horn and immediately recognized as Lang's van. He and his partner put h under arrest Kurt and Dave for having stolen a police car.
However, Paxton along with Gale went to Pym Technologies facilities where something weird was happening. As they drove to police headquarters, they received a call from a family who informed a battle between two strange beings was happening at home. Upon arrival, they discovered that it was Lang, who tried to explain what happened; but Gale using an electric device left him unconscious. Back in the car, Paxton and Gale received another important notice, but this time the events were taking place at Maggie's home. Not knowing what was happening inside the house, Paxton went and found how Lang bravely protected Cassie from Cross. Paxton took Cassie and put her behind him trying to defend her from the attacker. Paxton and Cassie were saved by Scott who decided to become microscopic in order to destroy the Yellowjacket suit.
With the battle ended and Cassie safe, he told Lang that he had destroyed the top of the house, which Lang apologized. Days later, during a dinner Paxton informed Lang that all charges were dropped and he was now welcome to visit Cassie anytime he wants.