James O. Gesling joined the Food and Drug Administration (FDA) in 1956, when he graduated from Northwest Missouri State College. He Initially, he was an inspector in the FDA Kansas City District at first. Beginning in 1968, he was assistant director for regulations and administration of the FDA’s Bureau of Veterinary Medicine. He later became the Executive Officer of the Bureau of Veterinary Medicine.

When the National Institutes of Health (NIH) Division of Biologics Standards (DBS) moved to the FDA in 1972, Gesling became the Associate Director for Management and Compliance at what was then called the Bureau of Biologics.