John Baker was born around 1804 in County Down in present-day Northern Ireland. He married Susanna Walker around 1827, and they had at least five children: Samuel, born around 1828; Thomas, born on December 30, 1832; Joseph, born around 1839; Elizabeth, born on June 2, 1842; and James, born around 1846. The family immigrated to America aboard the brig Amelia in 1831, and by that fall, they had settled in Pittsburgh, Pennsylvania. He earned a living as a laborer. An early biographer described him as a "man of unusual attainments and high character. His library consisted of religious and theological works and encyclopedias." They lived in Pittsburgh until around 1842, when they moved to Findley, Pennsylvania. He worked as a farmer there, and by 1850, he owned $790 of real estate. He was a member of the local Reformed Presbyterian Church, although two of his sons eventually converted to Catholicism. He died in 1857.