John Riley Tanner was born on a farm near the town of Boonville in Warrick County, Indiana. His family moved to Illinois when he was a child, and he grew up on a farm near Carbondale. He enlisted in the 98th Illinois Infantry at the age of 19, during the Civil War, and saw service with Sherman's army. When the 98th Infantry was mustered out of service in June 1865, Tanner was transferred to the 61st Illinois Infantry, and was mustered out of service later that year. He then returned to southern Illinois and settled in Clay County, where he farmed and entered into a partnership with his brother in a milling and lumber business. He married Lauretta Ingrahm, but was widowed.
In 1896 Tanner was elected as the 21st Governor of Illinois, and he served from 1897 until 1901. He was one of the most remarkable governors of the late nineteenth century.
Tanner was the first governor in the country to be openly neutral in labor disputes, gaining national notoriety for his actions in a series of coal mine disputes. With the Spanish-American War looming, he was the only governor to raise and combat-equip an Illinois National Guard unit of African American soldiers led by African American officers. In 1897 the Illinois State Association in DC honored Tanner with a reception that also celebrated the first Inauguration of President William McKinley and Vice President Theodore Roosevelt.