Keatley was born in [[Boalsburg, Pennsylvania]] to and John Gregg and Emily Hubler Keatley. After attending schools in [[Bellefonte, Pennsylvania]], he read law there with [[Andrew Gregg Curtin]], a relative of Keatley's father who was elected governor in 1860.<ref name=conference>{{cite book|url=https://babel.hathitrust.org/cgi/pt?id=uc1.aa0000940320&view=1up&seq=235&skin=2021|title=Judges of the United States|work=Judicial Conference of the United States|year=1978|access-date=2021-12-16}}</ref> Keatley was admitted to the bar that year. Soon after, he became the editor of ''The Blair County Whig'', a pro-Lincoln newspaper.<ref name=ia>{{cite journal|url=https://www.legis.iowa.gov/docs/publications/AIO/attachments/781173_955407.pdf|title=John H. Keatley|journal=The Annals of Iowa|volume=7|number=3|year=1905}}</ref>
He joined the [[125th Pennsylvania Infantry Regiment]] as an administrator, and was an assistant adjutant general on the staff of [[Jacob C. Higgins]] during the [[Gettysburg campaign]]. After working for [[Ulysses S. Grant|General Grant]] in the waning days of the [[American Civil War|Civil War]], Keatley worked with the [[Freedmen's Bureau]] in southeastern Virginia and was a judge in a military court in [[Norfolk, Virginia|Norfolk]].<ref name=ia/>
