Garner was born in Lancaster, Pennsylvania on 15 May 1829, to Virginia Montrose and Benjamin Garner, a couple of second-generation English American settlers. While pursuing a political career in his home town, he met Jo Muncher; the two would later move to Omaha, Nebraska and get married. After the marriage, Garner largely abandoned the political activity, until 1875, when he, along with Edwin Lanceton and Daniel Bergmann, established the Rioblancoan Independence Congress (later Home Guard Party), after statehood ambitions were thwarted by President Andrew Johnson.