John Poage Williamson was born in Lac qui Parle, Minnesota, on October 27, 1835. He completed undergraduate studies at Marietta College, Ohio, in 1857. In 1860, he earned his Master of Arts degree from Lane Theological Seminary in Ohio. He married Sarah A. Van Nice on April 27, 1866. The couple had at least one child, Mabel Ruth (born 1877-died 1885).
Licensed to preach by the Presbyterian Church in 1859, he was ordained the following year. Williamson chose to work with the Native Americans in the West. From his missionary father, he had learned how to speak Dakota as a child and was dedicated to preaching in that language. He was a missionary to the Dakota Indians from 1860 to 1898, and worked at many sites. Those sites included the Lower Sioux Agency, Minnesota, from 1860 to 1862; Fort Snelling from 1862 to 1863; Crow Creek, South Dakota, from 1863 to 1866; Santee Agency, Nebraska, from 1866 to 1869; and the Yankton Agency, South Dakota, from 1869 to 1898.
Williamson's other accomplishments include acting as the Special U.S. Agent for the Flandreau Indians form 1873 to 1878, and writing many publications. In 1871, he started a Native American publication entitled Iape Oaye. Williamson also wrote books, including Oowa Wowapi, Dakota Odowan, Dakota Hymn and Tune Book, An English-Dakota Dictionary, Dakota & English Ieska Wowapi, Dakota Mission: Past and Present, and The History of the Dakota Presbytery. He received an honorary degree from Yankton College, South Dakota, in 1890. Williamson died on October 3, 1917.