John Geary studied civil engineering and law at Jefferson College, graduating in 1841. He began his career as a construction engineer for the Allegheny Portage Railroad. Geary served in the military during the Mexican–American War, rising to the rank of colonel. He held various political positions, including postmaster and mayor of San Francisco, and served as a delegate to the State Constitutional Convention. Geary was appointed governor of the Kansas Territory, where he attempted to maintain neutrality amidst proslavery conflicts. During the Civil War, he raised and commanded Pennsylvania infantry regiments, participating in numerous significant battles and being promoted to Brigadier General. After the war, Geary was elected Governor of Pennsylvania, where he focused on attacking the influence of railroads and opposing special interest legislation. His contributions to Freemasonry also played a role in his life and the Reconstruction era.

John Geary's political identity is marked by a blend of military valor and a staunch opposition to special interests, particularly railroads. His approach to governance in Kansas reveals a calculated strategy to maintain neutrality amidst violent conflict, while his later actions as Governor of Pennsylvania demonstrate a principled resistance to corporate influence. Geary's ideological stances, particularly his unexpected alliances and policy decisions, hint at a deeply strategic mind, balancing regional interests with broader national objectives.