Pat Leivy trains alongside Juan "Johnnie" Rico in the Earth Federation's Mobile Infantry at Camp Arthur Currie. Physically larger than many recruits, he endures a personal setback during training when his girlfriend ends their relationship, an event termed "女友兵变" or romantic betrayal in service. He witnesses Theodore C. Hendrick's disciplinary conflicts with Sergeant Zim. Unlike Hendrick, Leivy completes basic training. After graduation, he is assigned to active duty with K Company, serving in the same unit as Rico.

Leivy fights against the extraterrestrial Bugs, participating in combat operations including the assault on their homeworld Klendathu. He survives this major engagement and continues as an active squad member in Rico's combat team during subsequent missions, maintaining his role as a supporting squad member throughout the depicted events.